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A new blood-brain barrier (BBB) in vitro model of tilapia (Oreochromis niloticus) was successfully established by co-culture with brain microvascular endothelial cell line TVEC-01 and brain astrocyte cell line TA-02 of tilapia. Experiments with the expression levels of BBB-related genes, TEER value detection and 4-h water-leaking test have shown that the BBB in vitro model has an excellent barrier effect. In bacterial penetration experiments, the pathogenic strain of Streptococcus agalactiae was able to pass through the BBB in vitro model and initiate a series of immune responses, among which TA-02 contributed to the expression of pro-inflammatory cytokines and TVEC-01 contributed to the expression of anti-inflammatory cytokines, providing an excellent research tool and theoretical basis for further study of meningitis. Moreover, the qRT-PCR and transmission electron microscopy revealed that the pathogenic strain of S. agalactiae effectively penetrated the BBB in vitro model of tilapia during early-stage infection without destroying tight junction integrity. This suggested that, in the initial phases of infection, the pathogenic strain of S. agalactiae may breach the BBB via a transcellular pathway rather than a paracellular pathway. Summarily, a novel BBB in vitro model of tilapia was successfully designed and evaluated for reproducing alterations in brain infecting., Competing Interests: Conflicts of interest The authors declare that no conflict of interest exists., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Streptococcosis is the leading bacterial disease impacting Nile tilapia (Oreochromis niloticus) and causes substantial economic losses in China. This study assessed the resistance and tolerance of three Nile tilapia (88, 99, and NG) to Streptococcus agalactiae infection. Survival rates were monitored, and samples were collected from blood, liver, and spleen at 0, 1, 2, 5, 7, and 14 days post-infection. Serum biochemical parameters, hepatic antioxidant enzymes, and the expression of related antioxidant and immune genes were measured. Results showed that strain 88 had superior resistance, with the highest survival rate, reduced liver damage, and lower alanine aminotransferase and alkaline phosphatase levels at 1 and 5 days post-infection. This strain also had higher serum cholesterol and triglyceride levels between days 5 and 14. Antioxidant activities increased in all strains post-infection, with strain 88 showing significantly higher superoxide dismutase (SOD) activity and elevated catalase (CAT) and SOD gene expressions; this indicated enhanced control of reactive oxygen species and reduced tissue damage. Additionally, strain 88 exhibited lower levels of inflammatory markers (TNF-α, IL-1β, IL-10) with higher IgM levels and superior MHC-II expression during early infection, which demonstrated a strong immune response. These results indicate that strain 88 is a promising candidate for selective breeding to improve streptococcosis resistance in tilapia., Competing Interests: Declaration of competing interest All the authors do not have any possible conflicts of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Chemokines play crucial roles in the regulation of immune cell migration and development. The CXCL12/CXCR4 axis has been extensively studied in mammals, but its regulatory mechanism in teleost fish remains unclear. In this study, we used Nile tilapia (Oreochromis niloticus) as a teleost model to investigate the mediation of the CXCL12/CXCR4 axis in IgM+ B cells. Our findings demonstrate that the CXCL12/CXCR4 axis exhibits chemotactic activity on IgM+ B cells and promotes the phagocytosis of IgM+ B cells. Blocking CXCR4 severely impairs the chemotaxis and phagocytosis of IgM+ B cells in vitro and reduces the percentages and numbers of IgM+ B cells that migrate to peripheral blood after pathogen infection in vivo. This reduction in migration leads to a decrease in the inflammatory response, an increase in tissue bacterial load, and a decrease in survival rate. We also discovered that the evolutionarily conserved PI3K-AKT signaling pathway and Girdin are involved in the immune response during Streptococcus agalactiae infection. Inhibitors of the PI3K-AKT signaling pathway prevent the chemotaxis and phagocytosis of IgM+ B cells, impair the expression and phosphorylation levels of related proteins in vitro, and prevent IgM+ B cells chemotaxis into the peripheral blood after pathogen infection in vivo. Furthermore, CXCR4 blocking significantly downregulates the expression of AKT and Girdin. Overall, our study reveals the regulatory mechanism of the CXCL12/CXCR4 axis on IgM+ B cells via the PI3K-AKT signaling pathway in tilapia, suggesting that the functions of the CXCL12/CXCR4 axis in B cells may be conserved between mammals and teleost fish., (Copyright © 2024 by The American Association of Immunologists, Inc.)

Previous research has established that the formation of Gardnerella vaginalis (GV) biofilm is one of the primary reasons for bacterial vaginosis (BV) recurrence. This study was the first to explore the impact of Streptococcus agalactiae (group B Streptococcus, GBS) on GV biofilm in a co-culture scenario. The results revealed that GBS could significantly increased the GV biomass in 48-hours dual-species biofilms. The luxS gene of GBS was significantly higher in dual-species biofilm, while knockdown of the luxS gene resulted in a significant decrease in mono- and dual-species biofilms. Meanwhile, in vitro addition of AI-2 (product of luxS gene) substantially increased biofilm biomass. Furthermore, we found that the expression of two genes related to biofilm formation was notably elevated in GV after receiving AI-2 signals. Collectively, these findings suggest that GBS enhances GV biofilm formation via luxS/AI-2 in an in vitro co-culture model, which in turn may promotes recurrence of BV., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Nile tilapia (Oreochromis niloticus) is one of the important economic fish species cultured worldwide. However, Streptococcus agalactiae has emerged as a significant bacterial threat, severely impacting the economy of tilapia industry. The immune response underlying the resistance of tilapia to S. agalactiae are not well understood, hindering the reasonable evaluation of breeding and the formulation of effective strategies. In this study, we investigated the differences in T-cell immunity between S. agalactiae-resistant and -susceptible tilapia. Compared with susceptible tilapia, resistant tilapia exhibited a higher percentage of T cells and BrdU + T cells during infection, indicating a superior proliferative capacity. Whether infected or not, T cells from resistant fish demonstrated a greater ability to resist apoptosis. Additionally, T cell effector genes, including interleukin (IL)-2, interferon (IFN)-γ, perforin A, and granzyme B were expressed at higher levels in resistant tilapia after infection. Along with these T-cell immune responses, resistant fish showed more effective clearance of infection. Our study elucidates the T-cell immune responses in resistant tilapia, which may contribute to the high resistance of tilapia to S. agalactiae, and provide valuable theoretical references for the selection and evaluation of disease-resistant fish strains in the future., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

IgY is an immunoglobulin primarily found in the serum and egg yolk of birds, amphibians, and reptiles. Recent years, IgY is considered to have a good application prospect in the immunodiagnostics and passive immunotherapy of aquatic diseases. In this study, we prepared a specific IgY against Streptococcus agalactiae in tilapia after immunizing the hens for 4 times. The result of ELISA detection showed that the IgY titers in water-soluble fraction (WSF) after 6 weeks of immunization reached 1:51200 and last for 4 weeks. Western blot (WB) analysis data showed that the specific IgY could recognize the target band, the specific IgY showed a concentration-dependent inhibitory effect on the growth of S. agalactiae, altered cell wall structure and aggluted of S. agalactiae. The quantitative reverse transcription PCR (qRT-PCR) analysis data suggested that the specific IgY downregulated the expression of pro-inflammatory factors (IL-8, TNF-α), upregulated the anti-inflammatory factors (IL-10, TGF-β). In addition, the histopathological results showed that the specific IgY significantly decreased the pathological manifestations, dramatically improved the survival rates of tilapia in injection, feeding, and immersion experiments. Collectively, our findings demonstrated that the broad potential of specific IgY for the prevention and treatment of S. agalactiae infection in tilapia., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In the aquatic farming industry, understanding the factors affecting fish behavior is crucial, particularly in response to infections that compromise welfare and productivity. Swimming performance is a key life history trait critical to their ecology. This study explores the swimming behavior imbalance in Nile tilapia (Oreochromis niloticus, GIFT) post-infection with Streptococcus agalactiae (GBS), a common pathogen responsible for significant losses in aquaculture. We focused on how the microbiota-gut-brain axis influences the behavioral response of tilapia to GBS infection. Behavioral changes were quantified by measuring collision times and swimming speeds, which decreased significantly following infection. This behavioral downturn is mediated by alterations in the microbiota-gut-brain axis, evidenced by increased levels of monoamine neurotransmitters (serotonin, norepinephrine, and dopamine) in the brain and intestinal tissues. The study utilized pharmacological agents, the 5-HT 1A receptor agonist (8-OH-DPAT) and antagonist (WAY-100635), to investigate their efficacy in mitigating these behavioral and biochemical changes. Both agents partially restored normal behavior by adjusting neurotransmitter concentrations disrupted by GBS infection. Additionally, a notable increase in the relative abundance of Streptococcus within the gut microbiota of infected fish highlights the potential role of specific bacterial populations in influencing host behavior. This research provides novel insights into the complex interactions between pathogen-induced gut microbiota changes and Nile tilapia's behavioral outcomes, highlighting potential avenues for improving fish health management through microbiota-targeted interventions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

High mobility group protein B2 (HMGB2) is an abundant chromatin-associated protein with pivotal roles in transcription, cell proliferation, differentiation, inflammation, and tumorigenesis. However, its immune function in Nile tilapia (Oreochromis niloticus) remains unclear. In this study, we identified a homologue of HMGB2 from Nile tilapia (On-HMGB2) and investigated its functions in the immune response against streptococcus infection. The open reading frame (ORF) of On-HMGB2 spans 642 bp, encoding 213 amino acids, and contains two conserved HMG domains. On-HMGB2 shares over 80 % homology with other fish species and 74%-76 % homology with mammals. On-HMGB2 was widely distributed in various tissues, with its highest transcript levels in the liver and the lowest in the intestine. Knockdown of On-HMGB2 promoted the inflammatory response in Nile tilapia, increased the bacterial load in the tissues, and led to elevated mortality in Nile tilapia following Streptococcus agalactiae infection. Taken together, On-HMGB2 significantly influences the immune system of Nile tilapia in response to streptococcus infection., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Mobile genetic elements (MGEs) enable bacteria to acquire novel genes and traits. However, the functions of cargo genes within MGEs remain poorly understood. The cadmium resistance operon cadDX is present in many gram-positive bacteria. Although cadDX has been reported to be involved in metal detoxification, its regulatory mechanisms and functions in bacterial pathogenesis are poorly understood. This study revealed that cadDX contributes to cadmium resistance, oxidative stress resistance, and virulence in Streptococcus suis, an important zoonotic pathogen in pigs and humans. CadX represses cadD expression by binding to the cadDX promoter. Notably, cadX responds to H 2 O 2 stress through an additional promoter within the cadDX operon, mitigating the harmful effect of excessive cadD expression during oxidative stress. cadDX resides within an 11 K integrative and mobilizable element that can autonomously form circular structures. Moreover, cadDX is found in diverse MGEs, accounting for its widespread distribution across various bacteria, especially among pathogenic streptococci. Transferring cadDX into another zoonotic pathogen, Streptococcus agalactiae, results in similar phenotypes, including resistance to cadmium and oxidative stresses and increased virulence of S. agalactiae in mice. The new functions and regulatory mechanisms of cadDX shed light on the importance of the cadDX system in driving evolutionary adaptations and survival strategies across diverse gram-positive bacteria., (© 2024. The Author(s).)

Heme oxygenase-1 (HO-1), an inducible rate-limiting metabolic enzyme, exerts critical immunomodulatory functions by potential anti-oxidant, anti-inflammatory, and anti-apoptotic activities. Although accumulative studies have focused on the immune functions of HO-1 in mammals, the roles in fish are poorly understood, and the reports on involvement in the defensive and immune response are very limited. In this study, On-HO-1 gene from Oreochromis niloticus was successfully cloned and identified, which contained an open reading frame (ORF) of 816 bp and coded for a protein of 271 amino acids. The On-HO-1 protein phylogenetically shared a high homology with HO-1 in other teleost fish (76.10%-98.89 %) and a lowly homology with HO-1 in mammals (38.98%-41.55 %). The expression levels of On-HO-1 were highest in the liver of healthy tilapias and sharply induced by Streptococcus agalactiae or Aeromonas hydrophila. Besides, On-HO-1 overexpression significantly increased non-specific immunological parameters in serum during bacterial infection, including LZM, SOD, CAT, ACP, and AKP. It also exerted anti-inflammatory and anti-apoptotic effects in response to the immune response of the infection with S. agalactiae or A. hydrophila by upregulating anti-inflammatory factors (IL-10, TGF-β), autophagy factors (ATG6, ATG8) and immune-related pathway factors (P65, P38), and down-regulating pro-inflammatory factors (IL-1β, IL-6, TNF-α), apoptotic factors (Caspase3, Caspase9), pyroptosis factor (Caspase1), and inflammasome (NLRP3). These results suggested that On-HO-1 involved in immunomodulatory functions and host defense in Nile tilapia., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024. Published by Elsevier Ltd.)

In the present study, 59 autochthonous bacteria were isolated from the intestine of tilapia. Following enzyme producing activity, antagonistic ability, hemolytic activity, drug sensitivity assessments, and in vivo safety evaluation, 7 potential probiotic strains were screened out: Bacillus tequilensis BT0825-2 (BT), Bacillus aryabhattai BA0829-3 (BA1), Bacillus megaterium BM0505-6 (BM), Bacillus velezensis BV0505-11 (BV), Bacillus licheniformis BL0505-18 (BL), B. aryabhattai BA0505-19 (BA2), and Lactococcus lactis LL0306-15 (LL). Subsequently, tilapia were fed basal diets (CT) and basal diets supplemented with 10 8  CFU/g of BT, BA1, BM, BV, BL, BA2 and LL, respectively. After 56 days of continuous feeding, the growth parameters (weight gain, final weight, and specific growth rate) showed significant improvement (p < 0.05) in both BM and BA2 groups. The total cholesterol and triglycerides of serum were significantly decreased in BV and LL groups (p < 0.05). The superoxide dismutase, glutathione reductase, and lysozyme of BV, BA2 and LL groups were increased, and the malondialdehyde of BV group was significantly decreased. The villous height and amylase of midgut were increased in BV, BA2 and LL groups. In addition, the expression levels of ZO-1 and occludin genes in the midgut of tilapia were enhanced in BM, BV, BA2 and LL groups. The supplementation of probiotics reduced the abundance of Cyanobacteria and increased the abundance of Actinobacteria at the phylum level. At the genus level, the addition of probiotics increased the abundance of Romboutsia. Furthermore, improvement in the expression of immune-related genes were observed, including interleukin 1β, interleukin 10, tumor necrosis factor alpha, and transforming growth factor beta (p < 0.05). After challenging with S. agalactiae, the survival rates of BV, BA2 and LL groups were significantly higher than CT group (p < 0.05). Above results indicated that BM, BA2, BV and LL improved growth performance, gut health or immunity of tilapia, which can be applied in tilapia aquaculture., Competing Interests: Declaration of competing interest The authors have declared no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Various types of professional immune cells first emerge in fish and likely represent the primordial form and functions. Recent advancements revealed the direct connection between the central nervous system and the immune system in the mammalian brain. However, the specifics of brain-immune networks in the fish and the underlying mechanisms of teleost's brain against pathogen infection have not been fully elucidated. In this study, we investigated the distribution of markers representing cerebral cells associated with protection and professional lymphocytes in the seven major components of the Nile tilapia brain through RNA-Seq assay and observed the most dominant abundance in the medulla oblongata. The subsequent challenge test revealed the non-specific cytotoxic cells (NCCs) exhibited the strongest response against streptococcal infection of the brain. The presence of NCCs in the brain was then confirmed using immunofluorescence and the cytotoxic effects usually induced by NCCs under infection were determined as well. Collectively, these findings contribute significantly to comprehending the mechanism of fish neuroimmune interaction and enhancing our understanding of its evolutionary development., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Hou and Li.)

Streptococcosis, the most common bacterial disease of fish in recent years, is highly infectious and lethal, and has become an important factor hindering the healthy and sustainable development of aquaculture. Chicken egg yolk antibody (IgY) has the advantages of high antigen specificity, inexpensive and easy to obtain, simple preparation, no toxic side effects, and in line with animal welfare, which is a green and safe alternative to antibiotics. In this study, the potential of specific IgY in the treatment of gastrointestinal pathogens was explored by observing the effects of specific IgY on intestinal flora, pathological tissue, apoptosis, oxidative stress, and inflammatory response of tilapia. We used the specific IgY prepared in the early stage to feed tilapia for 10 days, and then the tilapia was challenged with Streptococcus agalactiae. The results showed that feeding IgY before challenge had a small effect on the intestinal flora, and after challenge specific IgY decreased the proportion of Streptococcus and increased the diversity of the intestinal flora; in histopathology, specific IgY decreased tissue damage and maintained the integrity of tissue structure. Further study found that specific IgY can reduce intestinal epithelial cell apoptosis and reduce caspase activity; at the same time, the content of MDA was decreased, and the activities of SOD, CAT, GSH-Px and GR were increased. In addition, specific IgY can down-regulate the expression levels of IL-8 and TNF-α genes and up-regulate the expression levels of IL-10 and TGF-β. The results of this study showed that specific IgY could improve the intestinal flora of tilapia infected with Streptococcus agalactiae, reduce intestinal cell apoptosis, oxidative stress injury and inflammatory response, thereby reducing tissue damage and protecting the health of tilapia. Overall, specific IgY can be further explored as a potential antibiotic alternative for gastrointestinal pathogen infections., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Objectives: The aim of this study was to quantify and identify metabolites of Ice Nucleation Active (INA) bacteria as an anti-biofilm agent against biofilms of fish pathogens such as Aeromonas hydrophila and Streptococcus agalactiae., Results: Ice nucleation active bacteria, which have the ability to catalyze ice nucleation, isolated from rainwater in previous studies, were used. All INA isolates were tested in several assays, including the antimicrobial test, which uses streptomycin as the positive control and none of the isolates were found positive in the antimicrobial test. As for the quorum quenching assay, it was found that four out of ten isolates were able to disturb the communication system in Chromobacterium violaceum wild type, which was used as the indicator bacteria. On the next assay, all ten isolates were tested for Biofilm Inhibition and Destruction and showed anti-biofilm activity with the highest percentage inhibition of 33.49% by isolate A40 against A. hydrophila and 77.26% by isolate A19 against S. agalactiae. C1 performed the highest destruction against A. hydrophila and S. agalactiae, with percentages of 32.11% and 51.88%, respectively. As for the GC-MS analysis, supernatants of INA bacteria contain bioactive compounds such as sarcosine and fatty acids, which are known to have antibiofilm activity against several biofilm-forming bacteria. Through 16s rRNA sequencing, identified bacteria are from the Pantoea, Enterobacter, and Acinetobacter genera. As for the conclusion, ice nucleation active bacteria metabolites tested showed positive results against pathogenic bacteria Aeromonas hydrophila and Streptococcus agalactiae in destructing and inhibiting biofilm growth., (© 2024. The Author(s).)

Fish rely on innate immune system for immunity, and nucleotide-binding oligomerization domain-like receptors (NLRs) are a vital group of receptor for recognition. In the present study, NOD1 gene was cloned and characterized from golden pompano Trachinotus ovatus, a commercially important aquaculture fish species. The ORF of T. ovatus NOD1 was 2820 bp long, encoding 939 amino acid residues with a highly conserved domains containing CARD-NACHT-LRRs. Phylogenetic analysis revealed that the T. ovatus NOD1 clustered with those of fish and separated from those of birds and mammals. T. ovatus NOD1 has wide tissue distribution with the highest expression in gills. Bacterial challenges (Streptococcus agalactiae and Vibrio alginolyticus) significantly up-regulated the expression of NOD1 with different response time. The results of T. ovatus NOD1 ligand recognition and signaling pathway analysis revealed that T. ovatus NOD1 could recognize iE-DAP at the concentration of ≧ 100 ng/mL and able to activate NF-κB signaling pathway. This study confirmed that NOD1 play a crucial role in the innate immunity of T. ovatus. The findings of this study improve our understanding on the immune function of NOD1 in teleost, especially T. ovatus., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Non-specific cytotoxic cells (NCCs) are vital immune cells involved in teleost's non-specific immunity. As a receptor molecule on the NCCs' surface, the non-specific cytotoxic cell receptor protein 1 (NCCRP-1) is known to play a crucial role in mediating their activity. Nevertheless, there have been limited studies on the signal molecule that transmits signals via NCCRP-1. In this study, a yeast two-hybrid (Y2H) library of tilapia liver and head kidney was constructed and subsequently screened with the bait vector NCCRP-1 of Oreochromis niloticus (On-NCCRP-1) to obtain a C-type lectin (On-CTL) with an interacting protein sequence. Consequently, the full-length sequence of On-CTL was cloned and analyzed. The expression analysis revealed that On-CTL is highly expressed in the liver and is widely distributed in other tissues. Furthermore, On-CTL expression was significantly up-regulated in the brain, intestine, and head kidney following a challenge with Streptococcus agalactiae. A point-to-point Y2H method was also used to confirm the binding between On-NCCRP-1 and On-CTL. The recombinant On-CTL (rOn-CTL) protein was purified. In vitro experiments demonstrated that rOn-CTL can up-regulate the expression of killer effector molecules in NCCs via its interaction with On-NCCRP-1. Moreover, activation of NCCs by rOn-CTL resulted in a remarkable enhancement in their ability to eliminate fathead minnow cells, indicating that rOn-CTL effectively modulates the killing activity of NCCs through the NCC receptor molecule On-NCCRP-1. These findings significantly contribute to our comprehension of the regulatory mechanisms governing NCC activity, paving the way for future research in this field., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Zinc is one of the essential microelements for the metabolism of animals. Zinc nanoparticles may have higher bioavailability due to their low specific surface area, facilitating absorption by fish. The present study aimed to evaluate the effects of supplementation with different zinc-based products on the growth and health of Nile tilapia Oreochromis niloticus. Zinc, in different sizes (nanoparticles or bulk) and forms (inorganic or organic), were used as a supplement in the tilapia diet at a dose of 15 mg kg feed -1 for 60 days. At the end of the feeding trial, production performance, hemato-immunological parameters, activity of antioxidant system enzymes, exposure to Streptococcus agalactiae and zinc concentration in the muscle were examined. After the bacterial challenge, the mean corpuscular hemoglobin concentration (MCHC) significantly increased in the fish treated with organic zinc, inorganic nano zinc, and organic nano zinc, while in the control group (inorganic zinc), MCHC remained unchanged. Regarding defense cells, dietary inorganic nano zinc increased the number of basophils (1.50 ± 1.10) compared to organic zinc (0.80 ± 0.90). Lymphocyte count increased after the challenge only in the organic zinc treatments (bulk and nanoparticles). Neutrophils decreased in the control (inorganic zinc) (2.20 ± 1.70) and inorganic nano zinc (2.60 ± 2.70) treatments after the challenge. When compared before and after the bacterial challenge, the plasma antimicrobial titer significantly increased after the bacterial challenge in all treatments. No significant differences were observed for total proteins, enzymes (SOD and CAT), cumulative survival and zinc deposition on fillet. In conclusion, organic zinc in nanoparticles or bulk size increased Nile tilapia innate defense during bacterial infection. However, the other parameters evaluated were not affected by zinc particle size or form (organic or inorganic), indicating that further evaluations should be conducted with organic zinc in nanoparticles or bulk size in the tilapia diet., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Bacterial ClpB is an ATP-dependent disaggregate that belongs to the Hsp100/Clp family and facilitates bacterial survival under hostile environmental conditions. Streptococcus agalactiae, which is regarded as the major bacterial pathogen of farmed Nile tilapia (Oreochromis niloticus), is known to cause high mortality and large economic losses. Here, we report a ClpB homologue of S. agalactiae and explore its functionality. S. agalactiae with a clpB deletion mutant (∆clpB) exhibited defective tolerance against heat and acidic stress, without affecting growth or morphology under optimal conditions. Moreover, the ΔclpB mutant exhibited reduced intracellular survival in RAW264.7 cells, diminished adherence to the brain cells of tilapia, increased sensitivity to leukocytes from the head kidney of tilapia and whole blood killing, and reduced mortality and bacterial loads in a tilapia infection assay. Furthermore, the reduced virulence of the ∆clpB mutant was investigated by transcriptome analysis, which revealed that deletion of clpB altered the expression levels of multiple genes that contribute to the stress response as well as certain metabolic pathways. Collectively, our findings demonstrated that ClpB, a molecular chaperone, plays critical roles in heat and acid stress resistance and virulence in S. agalactiae. This finding provides an enhanced understanding of the functionality of this ClpB homologue in gram-positive bacteria and the survival strategy of S. agalactiae against immune clearance during infection., (© 2024. The Author(s).)

Group B Streptococcus (GBS; also known as Streptococcus agalactiae) is an opportunistic bacterial pathogen that causes sepsis, meningitis, pneumonia, and skin and soft tissue infections in neonates and healthy or immunocompromised adults. GBS is well-adapted to survive in humans due to a plethora of virulence mechanisms that afford responses to support bacterial survival in dynamic host environments. These mechanisms and responses include counteraction of cell death from exposure to excess metal ions that can cause mismetallation and cytotoxicity, and strategies to combat molecules such as reactive oxygen and nitrogen species that are generated as part of innate host defence. Cytotoxicity from reactive molecules can stem from damage to proteins, DNA, and membrane lipids, potentially leading to bacterial cell death inside phagocytic cells or within extracellular spaces within the host. Deciphering the ways in which GBS responds to the stress of cytotoxic reactive molecules within the host will benefit the development of novel therapeutic and preventative strategies to manage the burden of GBS disease. This review summarizes knowledge of GBS carriage in humans and the mechanisms used by the bacteria to circumvent killing by these important elements of host immune defence: oxidative stress, nitrosative stress, and stress from metal ion intoxication/mismetallation., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)

Using the unique structures found in natural materials to produce new antibacterial drugs is crucial. Actinobacteria is well-known for its ability to produce naturally occurring chemicals with a variety of structural features that can be used as weapons against infectious bacteria. In the present study, the Streptomyces coeruleorubidus metabolites were characterized and their efficacy in suppressing Streptococcus agalactiae growth was carried out both in vitro and in vivo. The metabolites of S. coeruleorubidus were purified and identified as octasiloxane-hexadecamethyl (OHM). In vivo antibacterial activity of OHM revealed an inhibitory minimum concentration value of 0.5 μg/ml against S. agalactiae and induced ultrastructural cell changes revealed by scanning electron microscope. The safe concentration of OHM was determined as 0.8 mg/L for Nile tilapia. Four in vivo treatments were treated with 0 and 0.8 mg/L OHM and with or without challenge by S. agalactiae (1 × 10 7  CFU/mL) named control, OHM, S. agalactiae, and S. agalactiae + OHM groups. The OHM treatment improved the survival of Nile tilapia by 33.33% than S. agalactiae challenge group. Waterborne OHM treatment significantly mitigated the deleterious effects of S. agalactiae on hematological, hepato-renal functions, stress indicators, and antioxidant balance. OHM significantly alleviated nitric oxide levels, complement 3, IgM, and lysozyme activity, downregulation of liver antioxidant genes expression in S. agalactiae group. Furthermore, the addition of OHM to challenged fish with S. agalactiae-significantly reversed dramatic negative regulation of inflammatory, apoptosis, and immune related gene expression (caspase-3, bax, pcna, tnf-α, ifn-γ, il-8 il-1β, il-10, tgf-β, and bcl-2 in the Nile tilapia spleen. Additionally, the damaged hepatic and splenic structure induced by bacterial infection was restored with OHM treatment. Finally, S. coeruleorubidus metabolites (mainly OHM) revealed in vitro and in vivo antibacterial activity and showed alleviated effects on the physiological status of S. agalactiae infected tilapia., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

As a lymphocyte-specific surface receptor belonging to the cysteine-rich superfamily of scavenger receptors, CD6 acts as a pattern recognition receptor for microbial components and is involved in the regulation of inflammatory responses. However, the characteristics and functions of CD6 molecules in lower vertebrates represented by teleost fish are unknown. In this study, a CD6 homolog (designated OnCD6) was characterized from Nile tilapia (Oreochromis niloticus), and establishing its role as a PRRs that participates in immune recognition. OnCD6 contains an open reading frame of 1872 bp that encodes a peptide of 623 amino acids, and contains two conserved SR domain. Multiple sequence alignment revealed that OnCD6 shares a relatively high level of identity with those of other species. Transcriptional expression analysis revealed that OnCD6 was constitutively expressed in immunes tissues such as head kidney and thymus. The expression level of OnCD6 in mainly immune tissues were found significantly upregulated after the injection of Streptococcus agalactiae (S. agalactiae). Moreover, OnCD6 protein was located in the head kidney and brain, mainly over the plasma membrane of lymphocytes in these immune tissues. In vitro experiments showed that CD6 extracellular protein bound to and aggregated several Gram-positive and -negative bacterial strains through the recognition of bacterial surface conserved components LPS and LTA etc. In vivo experiments demonstrated that overexpression OnCD6 before S. agalactiae challenge significantly improved tilapia survival, and this was concomitant with reduced bacterial load and pro-inflammatory cytokines (IL-1β and TNF-α). Taken together, our results illustrated the function of CD6 molecular pattern recognition receptors (PRRs) is conserved and plays an important role in antibacterial infection., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024. Published by Elsevier Ltd.)

Background: Preterm birth is a leading cause of neonatal mortality, which is often complicated by intrauterine infection and inflammation. We have established a nonhuman primate model of Group B Streptococcus (GBS, Streptococcus agalactiae ) infection-associated preterm birth. Immune checkpoints are modulators of the immune response by activating or suppressing leukocyte function and are understudied in preterm birth. The objective of this study was to spatially profile changes in immune protein expression at the maternal-fetal interface during a GBS infection with a focus on immune checkpoints., Methods: Twelve nonhuman primates (pigtail macaques, Macaca nemestrina ) received a choriodecidual inoculation of either: 1) 1-5 X 10 8 colony forming units (CFU) of hyperhemolytic/hypervirulent GBS (GBSΔ covR , N=4); 2) an isogenic/nonpigmented strain (GBS Δ covR Δ cylE , N=4); or, 3) saline (N=4). A Cesarean section was performed at preterm labor or 3 days after GBS infection or 7 days after saline inoculation. Nanostring GeoMx® Digital Spatial Profiling technology was used to segment protein expression within the amnion, chorion, and maternal decidua at the inoculation site using an immuno-oncology panel targeting 56 immunoproteins enriched in stimulatory and inhibitory immune checkpoint proteins or their protein ligands. Statistical analysis included R studio, Kruskal-Wallis, Pearson and Spearman tests., Results: Both inhibitory and stimulatory immune checkpoint proteins were significantly upregulated within the chorioamniotic membranes and decidua (VISTA, LAG3, PD-1, CD40, GITR), as well as their ligands (PD-L1, PD-L2, CD40L; all p<0.05). Immunostaining for VISTA revealed positive (VISTA+) cells, predominantly in the chorion and decidua. There were strong correlations between VISTA and amniotic fluid concentrations of IL-1β, IL-6, IL-8, and TNF-α (all p<0.05), as well as maternal placental histopathology scores (p<0.05)., Conclusion: Differential regulation of multiple immune checkpoint proteins in the decidua at the site of a GBS infection indicates a major perturbation in immunologic homeostasis that could benefit the host by restricting immune-driven pathologies or the pathogen by limiting immune surveillance. Protein expression of VISTA, an inhibitory immune checkpoint, was upregulated in the chorion and decidua after GBS infection. Investigating the impact of innate immune cell expression of inhibitory immune checkpoints may reveal new insights into placental host-pathogen interactions at the maternal-fetal interface., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Manuel, Coleman, Orvis, Munson, Li, Kapur, Li, Li, Armistead, Rajagopal and Adams Waldorf.)

Nile tilapia (Oreochromis niloticus) occupies an important position in the culture of economic fish in China. However, the high mortality caused by streptococcal disease has had a significant impact on the tilapia farming industry. Therefore, it is necessary to clarify the immune mechanism of tilapia in response to Streptococcus agalactiae. As a hub in the natural immune signaling pathway, the junction molecule can help the organism defend against and clear pathogens and is crucial in the signaling pathway. In this study, the cDNA sequence of Nile tilapia TBK1 was cloned, and the expression profile was examined in normal fish and challenged fish. The cDNA sequence of the TBK1 gene was 3378 bp, and its open reading frame (ORF) was 2172 bp, encoding 723 amino acids. The deduced TBK1 protein contained an S&#95;TKc domain, a coiled coil domain and a ubiquitin-like domain (ULD). TBK1 had the highest homology with zebra mbuna (Maylandia zebra) and Lake Malawi cichlid fish (Astatotilapia calliptera), both at 97.59%. In the phylogenetic tree, TBK1 forms a large branch with other scleractinian fish. TBK1 expression was highest in the brain and lowest in the liver. LPS, Poly I:C, and S. agalactiae challenge resulted in significant changes in TBK1 expression in the tissues examined. The subcellular localization showed that TBK1-GFP was distributed in the cytoplasm and could significantly increase IFN-β activation. Pull-down results showed that there was an interaction between TBK1 and TRAF3 and an interaction between STING protein and TBK1 protein. The above results provide a basis for further investigation into the mechanism of TBK1 involvement in the signaling pathway., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Tilapia is one of the most economically important freshwater fish farmed in China. Streptococcosis outbreaks have been extensively documented in farmed tilapia species. Hybrid tilapia (Oreochromis niloticus ♀ × O. aureus ♂) exhibit greater disease resistance than Nile tilapia (O. niloticus) and blue tilapia (O. aureus). However, the molecular mechanism underlying the enhanced tolerance of hybrid tilapia is still poorly understood. In this study, comparative transcriptome analysis was performed to reveal the different tolerance mechanisms to Streptococcus agalactiae in the three tilapia lines. In total, 1982, 2355, and 2076 differentially expressed genes were identified at 48 h post-infection in hybrid tilapia, Nile tilapia, and blue tilapia, respectively. Functional enrichment analysis indicated that numerous metabolic and immune-related pathways were activated in all three tilapia lines. The differential expression of specific genes associated with phagosome, focal adhesion, cytokine-cytokine receptor interaction, and toll-like receptor signaling pathways contributed to the resistance of hybrid tilapia. Notably, immune response genes in hybrid tilapia, such as P38, TLR5, CXCR3, CXCL12, PSTPIP1, and TFR, were generally suppressed under normal conditions but selectively induced following pathogen challenge. These results expand our knowledge of the molecular mechanisms underlying S. agalactiae tolerance in hybrid tilapia and provide valuable insights for tilapia breeding programs., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The antibacterial activity of aqueous (AE) or ethanolic extracts (EE) of caper (Capparis spinosa) against Streptococcus agalactiae was evaluated in vitro. Both caper extracts showed antagonistic activity against S. agalactiae and the inhibition zones in case of ethanolic extracts were larger than those of aqueous ones. Additionally, TEM investigations show that S. agalactiae cells treated with both C. spinosa extracts were damaged and degraded and this damage was greater in case of ethanolic extract. Another study was done to assess the promotion effects of dietary caper (C. spinosa) extracts on growth, antioxidant and immune activity, and inflammation cytokine responses of Nile tilapia (Oreochromis niloticus) and its resistance to S. agalactiae infection. However, fish (40 ± 2 g) were fed on diets containing 1.0 and 2.0 g/kg feed of each caper extract as well as the control group (free of caper) for 6 weeks. Fish were intraperitoneally injected (IP) with Streptococcus agalactiae at the end of the feeding trial, and fish mortality was tracked for additional ten days. Compared with other treatments, fish fed on 2.0 g EE/kg feed had higher counts of white and red blood cells as well as higher hemoglobin levels accompanied with lower AST and ALT activities. Antioxidant (superoxide dismutase and catalase activities) and immune, total protein, globulin, lysozyme, and immunoglobulin M) indices were increased along with significant decline in MDA levels in both caper extracts treated fish groups compared to the control group. Significant promotion in fish growth was affected positively with the increase in both caper extracts; particularly, the larger fish growth was observed in the treatment of 2.0 g EE/kg feed. Expressions of IL-1β and IL-8 were declined; meanwhile levels of IL-10, SOD and CAT genes were upregulated in fish fed on 2.0 g EE/kg feed compared to other groups. After being challenged with S. agalactiae infection, fish survival was considerably (P < 0.05) greater in fish groups that fed on diets with caper extracts; particularly 2.0 g EE/kg feed (75%); while all fish fed on the control one were dead. According to these findings, the antioxidant and immune response of Nile tilapia fingerlings is stimulated by ethanolic extract of caper (2.0 g/kg feed), which also enhanced the growth performance and fish resistance to S. agalactiae infection., Competing Interests: Declaration of competing interest Authors declare that they have no conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Apolipoprotein E (ApoE), a critical targeting protein, has been found to play an essential role in the protection against infection and inflammation. However, the immune functions of ApoE against bacterial infection in fish have not been investigated. In this study, a full-length cDNA for ApoE, named On-ApoEb was cloned from Oreochromis niloticus. The predicted cDNA sequence was 831bp in length and coded for a protein of 276 amino acid residues, which shared 63.87%-98.55% identity with ApoEb from other fishes, and about 22% identity with ApoEb from mammals. On-ApoEb from O. niloticus was highly expressed in the liver and could be activated in the tissues (liver, spleen, brain, and intestine) after infection with Streptococcus agalactiae. Moreover, the results revealed that On-ApoEb could decrease the expression levels of pro-inflammatory factors, immune-related pathways, and apoptosis, while increasing the expression levels of anti-inflammatory factors. Furthermore, On-ApoEb was noted to improve the survival rate and reduce the bacterial load in the liver and spleen. These results suggested that On-ApoEb was connected with immune response and had anti-inflammation and anti-apoptosis activities., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023. Published by Elsevier Ltd.)

Interleukin 8 (IL8) is vital in promoting inflammation and is a crucial mediator in various physiopathological processes while influencing immunological function. The effect of IL8 on the immunological response to acute bacterial infections in Nile tilapia (Oreochromis niloticus) remains unknown. This work found an IL8 gene from Nile tilapia (On-IL8). It includes a 285 bp open reading frame and codes for 94 amino acids. The transcript levels of On-IL8 were highest in the head-kidney tissue and sharply induced by Streptococcus agalactiae and Aeromonas hydrophila. Besides, in vitro experiments revealed that On-IL8 regulated a variety of immunological processes and promoted inflammatory responses. Moreover, On-IL8 suppressed the NF-κB signaling pathway, consistent with in vitro results. These significant findings serve as the basis for further investigation into how IL8 confers protection to bony fish in opposition to bacterial infections., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Nile tilapia (Oreochromis niloticus) is one of the major food fish worldwide. The farming business, on the other hand, has faced considerable obstacles, such as disease infestations. Toll-like receptors (TLRs) play an important function in the activation of the innate immune system in response to infections. Unc-93 homolog B1 (UNC93B1) is a key regulator of nucleic acid (NA)-sensing TLRs. Here the UNC93B1 gene, which was cloned from Nile tilapia tissue for this investigation, had the same genetic structure as a homologous gene in humans and mice. Phylogenetic analysis revealed that Nile tilapia UNC93B1 clustered with UNC93B1 from other species and separately from the UNC93A clade. The gene structure of the Nile tilapia UNC93B1 was found to be identical to that of human UNC93B1. Our gene expression studies revealed that Nile tilapia UNC93B1 was highly expressed in the spleen, followed by other immune-related tissues such as the head kidney, gills, and intestine. Moreover, Nile tilapia UNC93B1 mRNA transcripts were up-regulated in vivo in the head kidney and spleen tissues from poly I:C and Streptococcus agalactiae injected Nile tilapia, as well as in vitro in LPS stimulated Tilapia head kidney (THK) cells. The Nile tilapia UNC93B1-GFP protein signal was detected in the cytosol of THK cells and was co-localized with endoplasmic reticulum and lysosome but not with mitochondria. Moreover, the results of a co-immunoprecipitation and immunostaining analysis showed that Nile tilapia UNC93B1 can be pulled down with fish-specific TLRs such as TLR18 and TLR25 from Nile tilapia, and was found to be co-localized with these fish-specific TLRs in the THK cells. Overall, our findings highlight the potential role of UNC93B1 as an accessory protein in fish-specific TLR signaling., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

CD27 is a member of the TNF-receptor superfamily and plays various roles in immunities. However, the detailed information and mechanism of CD27 in bony fish immunity remain unclear. Therefore, in this research, certain interesting roles of CD27 in Nile tilapia (On-CD27) were determined. On-CD27 was largely expressed in the immune organs, head kidney, and spleen, and was sharply induced during bacterial infection. The in vitro tests suggested On-CD27 was involved in regulating inflammatory responses, activating immune-related signal pathways, and inducing apoptosis and pyroptosis progress. The scRNA data and in vivo experiments indicated that On-CD27 is mainly expressed in CD4 + T cells and involved in both innate and adaptive immunities. The present data provide a theoretical principle for further research on the mechanisms of CD27 in the innate and adaptive immunities of fish., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023. Published by Elsevier Ltd.)

Apolipoprotein A-I (ApoA-I) is a lipoprotein involved in a variety of physiological and pathological processes. However, the immunomodulatory functions of ApoA-I in fish are not well understood. In this study, ApoA-I from Nile tilapia (Oreochromis niloticus) (On-ApoA-I) was identified, and its function in bacterial infection was investigated. The open reading frame of On-ApoA-I is 792 bp, which codes for a protein containing 263 amino acids. On-ApoA-I shared over 60% sequence similarity with other teleost fish and more than 20% with mammalian ApoA-I. On-ApoA-I was found to be highly expressed in the liver and significantly induced during Streptococcus agalactiae infection by qRT‒PCR analysis. Furthermore, invivo studies revealed that recombinant On-ApoA-I protein could suppress inflammation and apoptosis and improve the likelihood of surviving bacterial infection. Additionally, On-ApoA-I showed invitro antimicrobial properties against Gram-positive and Gram-negative bacteria. These findings offer a theoretical basis for further investigations into the role of ApoA-I in fish immunology., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023. Published by Elsevier Ltd.)

Application of novel trend comprising antioxidant phytogenics is aiming to minimize the stress related factors and associated diseases in intensive fish culturing. Today, the concept of exploiting and protecting natural antioxidants represents a paradigm shift for the aqua feed industry. Therefore, our principal goal targeting liposome as a novel nanocarrier for curcumin is directed to attain superior performance, fillet antioxidant stability and bacterial resistance in Nile tilapia. A total of 500 Nile tilapia fingerlings (average body weight, 10.27 ± 0.10 g) assigned into five experimental groups in 25 glass aquaria of 120 L capacity at the density 20 fish/aquaria. The experimental groups were supplemented with varying doses of liposomal curcumin-NPs, LipoCur-NPs (0, 5, 15, 25 and 35 mg/kg diet) were reared for 12 weeks and later Streptococcus agalactiae (S. agalactiae) challenged model was performed. Inclusion of LipoCur-NPs (25 and 35 mg/kg diet) had the most prominent impact on Nile tilapia growth rate and feed conversion ratio. The immune boosting outcomes post supplementing 35 mg/kg diet of LipoCur-NPs were evidenced by higher myeloperoxidase, lysozyme and total immunoglobulin levels. Even after 4 weeks frozen storage, LipoCur-NPs at the dose of 35 mg/kg diet prominently increased (P < 0.05) the fillet scavenging capability for free radicals (1,1-diphenyl-2-picrylhydrazyl and 2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) with an inverse reduction in lipid peroxidation biomarker (malondialdehyde). Notably, upregulation of GSH-Px, CAT, and SOD genes in fillet of 35 mg/kg LipoCur-NPs fed fish coordinated with higher T-AOC and lower oxidative markers (ROS and H 2 O 2 ). Post S. agalactiae challenge, higher supplementation levels of LipoCur-NPs (35 mg/kg diet) greatly attenuated the expression of its vital virulence genes (cfb, fbsA and cpsA) with higher expression of Igm, CXC-chemokine and MHC genes. Concordantly, downregulation of inflammatory markers (IL-1β, TNF-α and IL-8) and upregulation of anti-inflammatory ones (IL-10 and TGF-β) were remarkably documented. Based on these findings, the innovative curcumin loaded liposome was considered a novel multitargeting alternative not only playing an imperative role in Nile tilapia growth promotion and fillet stability upon storage, but also protecting efficiently against S. agalactiae., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Aquatic pollutants, including cadmium (Cd), cause oxidative stress on aquatic animals. The use of probiotics, including microalgae as a feed additive to alleviate the toxic impacts of heavy metals, is a much more interesting point. Hence, the current study investigated the oxidative stress and immunosuppression in Nile tilapia (Oreochromis niloticus) fingerlings caused by Cd toxicity as well as the preventive function of dietary Chlorella vulgaris against Cd toxicity. Accordingly, fish were fed on 0.0 (control), 5, and 15 g/kg diet of Chlorella up to satiation thrice a day, along with being exposed to 0.0 or 2.5 mg Cd/L for 60 days. Following the experimental procedure, fish from each group were intraperitoneally injected with Streptococcus agalactiae, and their survivability was observed for further ten days. Chlorella-supplemented diets meaningfully (P < 0.05) boosted the antioxidative capability of fish, which was evidenced by higher activities of hepatic superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione-S-transferase (GST) as well as higher levels of reduced glutathione (GSH) along with significant reductions in hepatic malondialdehyde levels. Moreover, the innate immunity indices [phagocytic activity (PA), respiratory burst activity (RBA), and alternative complement activity (ACH50)] were significantly higher in Chlorella-fed fish, particularly in the group of 15 g/kg diet. Additionally, serum of Chlorella-fed fish showed potent bactericidal activities against S. agalactiae, particularly at the treatment of a 15 g/kg diet. Feeding Chlorella diets to Nile tilapia fingerlings upregulated SOD, CAT, and GPx genes expression alongside the down-regulation of IL-1β, IL-8, IL-10, TNF-α, and HSP70 genes expression. Conversely, Cd toxicity caused oxidative stress and suppressed the fish's innate immunity with upregulation of the expression of IL-1β, IL-8, IL-10, TNF-α, and HSP70 genes. Feeding Cd-exposed fish on Chlorella-containing diets attenuated these adverse effects. The current research revealed that supplementing feeds with the treatment of 15 g/kg diet of C. vulgaris supports the antioxidant-immune responses and alleviates the Cd toxicity effects on Nile tilapia fingerlings., Competing Interests: Declaration of competing interest Authors declare that they have no conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

CD209 plays significant roles in pathogen recognition, innate and adaptive immunity, and cell-cell interactions. In the present study, a CD209 antigen-like protein E from Nile tilapia (Oreochromis niloticus) (designated as OnCD209E) was identified and characterized. OnCD209E contains an open reading frame (ORF) of 771 bp encoding a 257 amino acid protein, as well as the carbohydrate recognition domain (CRD). Multiple sequence analysis exhibits that the amino acid sequence of OnCD209E was relatively high homologous to that of partial fish, especially the highly conserved CRD, in which four conserved disulfide-bonded cysteine residues, WIGL conserved motif and two Ca 2+ /carbohydrate-binding sites (EPD and WFD motifs) were founded. Quantitative real-time PCR and Western Blot revealed that OnCD209E mRNA/protein is generally expressed in all tissues examined, but with wealth in head kidney and spleen tissues. The mRNA expression of OnCD209E was significantly increased in brain, head kidney, intestine, liver, and spleen tissues in response to the stimulation with polyinosinic-polycytidylic acid, Streptococcus agalactiae and Aeromonas hydrophila in vitro. Recombinant OnCD209E protein exhibited detectable bacterial binding and agglutination activity against different bacteria as well as inhibited the proliferation of tested bacteria. Subcellular localization analysis revealed that OnCD209E was mostly localized in the cell membrane. Moreover, overexpression of OnCD209E could activate nuclear factor-kappa B reporter genes in HEK-293T cells. Collectively, these results demonstrated that CD209E may potentially involve in immune response of Nile tilapia against bacterial infection., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023. Published by Elsevier Ltd.)

CD166 is a member of the immunoglobulin superfamily of cell adhesion molecules, and its mediated adhesion plays a crucial role in different physiological and pathological phenomena, especially related to leukocyte extravasation, immune synapse stability, T cell activation and proliferation. In this study, CD166 was identified from Nile tilapia (Oreochromis niloticus, OnCD166). OnCD166 contains an open reading frame of 1671 bp that encodes a peptide of 556 amino acids, and contains five consecutive extracellular immunoglobulin domains. It's tissue distribution and expression patterns after S. agalactiae challenge were also investigated. OnCD166 is widely distributed in various tissues of healthy tilapia. After Streptococcus agalactiae challenge, OnCD166 expressions were significantly up-regulated in all tested immune tissues. Meanwhile, the recombinant OnCD166 (rOnCD166E) protein showed strong agglutinating activities against both Gram-negative bacteria and Gram-positive bacteria. Moreover, rOnCD166E could promote phagocytosis of macrophages. Taken together, our results illustrated that OnCD166 might as a receptor involved in the immune recognition and phagocytosis against invading pathogen, which play important roles in the immune responses of Nile tilapia against bacterial pathogens., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

C-type lectin (CLEC) is a family of carbohydrate-binding protein that has high affinity for calcium and mediates multiple biological events including adhesion between cells, the turnover of serum glycoproteins, and the innate immune system's reaction to prospective invaders. However, it's ill-defined for how CLEC effects bony fish's innate immunity to bacterial infection. Therefore, CLEC12B, a member of the C-type lectin domain family, was found in Nile tilapia (Oreochromis niloticus) and its functions in bacterial infection were examined. The OnCLEC12B consist of a C-type lectin domain, a transmembrane domain, and a hypothetical protein of 308 amino acids that encoded by 927 bp basic group. Besides, the OnCLEC12B protein have a series of highly conserved amino acid sites with other CLEC12B proteins. Subcellular localization showed that OnCLEC12B located in cell membrane. Transcriptional levels investigation showed that OnCLEC12B was extensively expressed in all selected organs and has high expression in the liver. The transcriptional levels of OnCLEC12B were induced by Streptococcus agalactiae and Aeromonas hydrophila in the liver, spleen, head kidney, brain, and intestine. Afterward, invitro study revealed that several kinds of pathogens could be bound and agglutinated by recombinant protein of OnCLEC12B (rOnCLEC12B). Moreover, rOnCLEC12B could not only promote the proliferation of monocytes/macrophages but also encourage its phagocytosis on S.agalactiae and A.hydrophila, and its over-expression could significantly suppress the activation of the NF-κB pathway. Summarily, our results indicated that OnCLEC12B gets involved in fish immunization activities to pathogens infection., Competing Interests: Declaration of competing interest The authors affirm that no financial or commercial ties that might be viewed as having a conflict of interest existed during the research's execution., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

S100A12 is a member of S100 proteins family that induces pro-inflammatory response via ligating with the receptor for advanced glycation end products (RAGE) and subsequent activation of intracellular signal transduction pathways. But information about fish S100A12 remain largely unclear. In this study, the S100A12 homolog (On-S100A12) was identified from Nile tilapia (Oreochromis niloticus). On-S100A12 was mainly expressed in liver and intestine. After Streptococcus agalactiae infection in vivo, S100A12 significantly increased in brain, intestine, liver and head kidney, suggesting S100A12 might played roles in immune response. The further in vitro experiments found that recombinant protein of S100A12 (rOn-S100A12) upregulated the expression of IL1-β, TLR2, TNF-α and inhibited the expression of IL-10, indicating On-S100A12 promoted inflammatory response and activation of M1 macrophages. The present data lay a foundation to further explore the roles of fish S100 during immune defense and will also be beneficial for better understanding of fish immune-regulatory network., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Neural precursor cell-expressed developmentally downregulated gene 4 (NEDD4) was a member of HECT E3 ubiquitin ligases, which participated in various biological processes. In this study, a NEDD4 was identified and analyzed in Nile tilapia, Oreochromis niloticus (OnNEDD4) and its open reading frame was 2781 bp, encoding 926 amino acids. Three conserved structure features were found in OnNEDD4, including C2 domain, WW domains and HECT domain. OnNEDD4 was constitutively expressed in all examined tissues and the highest expression level was observed in thymus. After Streptococcus agalactiae stimulation, OnNEDD4 was significantly induced in several tissues, including thymus, intestine, blood and gill. Moreover, yeast two-hybrid assay shown OnNEDD4 could interact with extracellular region of OnCD40, but this interaction didn't affect the phagocytosis of monocytes/macrophages (MO/MΦ) to S. agalactiae and A. hydrophila. Taken together, the present study suggested that OnNEDD4 participate in CD40-mediated immune response excluding phagocytosis., (Copyright © 2022. Published by Elsevier Ltd.)

α-Melanocyte-stimulating hormone (α-MSH) is a well-studied neuropeptide controlling skin and hair color. Besides, numerous immunomodulation roles of α-MSH were recorded in humans and mice. However, the regulatory effects of α-MSH in teleost immunity haven't been well elucidated. In this study, several precursor molecules of α-MSH (POMCs) and its receptors (MCRs) in Nile tilapia (Oreochromis niloticus) were characterized, and their expression characteristics and specific functions on antibacterial immunity were determined. Overall, POMCs and MCRs were principally detected in the brain, skin, and liver, and were remarkably promoted post Streptococcus agalactiae infection. However, tiny POMCs and MCRs were observed in tilapia immune organs (head kidney and spleen) or lymphocytes, and no evident immunomodulation effect was detected in vitro. Moreover, the in vivo challenge experiments revealed that α-MSH protects tilapia from bacterial infection by regulating responses in the brain and intestine. This study lays theoretical data for a deeper comprehension of the immunomodulation mechanisms of teleost α-MSH and the evolutional process of the vertebrate melanocortin system., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Pyroptosis is an inflammatory and programmed cell death initiated by the formation of the inflammasome, which consists of NLR, ASC, and Caspase. Pyroptosis has received growing attention due to its association with innate immunity and various diseases. However, the involvement and induction of the NLRCs and pyroptosis-related genes in fish immunity remain poorly studied. In this study, several NLRCs and pyroptosis-related genes in Nile tilapia (Oreochromis niloticus) were identified and characterized. Their involvement in bacterial infection and expression profiles in Nile tilapia lymphocyte responses were also assessed. Overall, three NLRC members (NOD1, NOD2, and NLRC3) and five pyroptosis-related genes (ASC1, Caspase1, Gsdme, NLRP3, and NLRP14) in Nile tilapia were cloned and characterized. The transcript levels of these molecules were broadly distributed in various tissues with comparatively high expression in the gills, intestine, and spleen. Their transcripts were also induced during Streptococcus agalactiae or Aeromonas hydrophila infection. Moreover, they were primarily expressed in T cells, NCCs, and Mo/Mφ and showed antibacterial and partially antiviral responses. The present study lays a theoretical foundation for further investigation of the pyroptosis mechanisms in fish as well as the evolution of the antiviral roles of pyroptosis in vertebrates., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Complement factor H (CFH), a multifunctional soluble complement regulatory protein, can bind to a variety of pathogens and play a crucial role in host innate immune defense. To explore the functional characteristics of CFH (OnCFH) in Nile tilapia (Oreochromis niloticus), we cloned and characterized the open reading frame (ORF) of OnCFH in this study. The full-length of OnCFH ORF is 1359 bp, encoding 452 aa for a 48.85 kDa peptide, and its predicted structure containing six short complement-like repeats (SCRs). The analysis of tissue distribution showed that OnCFH was constitutively expressed in all tested tissues, with the highest in the liver. Upon Streptococcus agalactiae and Aeromonas hydrophila stimuli in vivo and in vitro, OnCFH mRNA transcript was significantly upregulated in head kidney tissue as well as head kidney monocytes/macrophages. Further, the recombinant OnCFH protein ((r)OnCFH) could bind to pathogenic bacteria in a dose-dependent. Moreover, it got involved in the regulation of inflammation as well as phagocytosis of monocytes/macrophages. The knockdown of OnCFH remarkably decreased the amount of bacteria in the head kidney. In summary, our data demonstrated that OnCFH could participate in the immune response of Nile tilapia against bacterial infection., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

As a pleiotropic cytokine mainly secreted by CD4 + T cells, interleukin (IL)-22 plays an important role in immune regulation and infection elimination. Despite IL-22 homologues have been identified in non-mammal, whether and how IL-22 participates in the adaptive immune response of early vertebrates have not been fully addressed. In this study, we identified an evolutionarily conserved IL-22 from Nile tilapia Oreochromis niloticus (defined as OnIL-22), proved by its properties regarding sequence, gene structure, functional domain, tertiary structure and phylogeny. IL-22 was broadly expressed in lymphoid-related tissues of tilapia, and with relatively higher levels in skin, gill, intestine and liver. The expression of OnIL-22 in spleen lymphocytes was markedly induced at the adaptive immune stage after Streptococcus agalactiae infection. Moreover, once lymphocytes were activated by PMA plus ionomycin or T-cell specific mitogen PHA in vitro, OnIL-22 expression was obviously up-regulated at both mRNA and protein levels. These results thus suggest that activated T cells produce IL-22 to take part in the adaptive immune response of tilapia. Furthermore, treatment of lymphocytes with recombinant OnIL-22 increased the expression of genes related to proliferation and survival, and further promoted the proliferation and reduced the apoptosis of lymphocytes during bacterial infection or T-cell activation. These cellular effects of IL-22 seem to be associated with JAK1/STAT3 axis downstream of IL-22, because IL-22 application not only elevated the mRNA expression of JAK1 and STAT3, but also enhanced their phosphorylation in lymphocytes. Altogether, we suggest that activated T cells produce IL-22 to promote lymphocyte proliferation and survival probability via JAK1/STAT3 signaling pathway, thus participating in adaptive immune response of Nile tilapia. Our study therefore provides helpful perspective for understanding the function and mechanism of adaptive immune system in teleost., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This study aimed to investigate the effects of Elephantopus scaber extract on the GIFT (genetic improvement of farmed tilapia) strain of Nile tilapia Oreochromis niloticus. A total of 800 tilapia with an initial body weight of 1.34 ± 0.09 g each were randomly divided into five groups. The tilapia in the control group (E0 group) were fed on a basal diet only. Meanwhile, tilapia in the four experimental groups were fed on a basal diet supplemented with 1 g/kg (E1 group), 3 g/kg (E2 group), 5 g/kg (E3 group), and 7 g/kg (E4 group) of E. scaber extract for 10 weeks. Results showed that the survival rate was higher in the experimental groups than in the control group. Compared with the control group, some growth parameters (FW, WGR, SGR, VSI, and HSI) were significantly improved in the E1 group and E2 group. The crude lipid content in the dorsal muscle and liver was lower in the E1 group than in the control group. After E. scaber extract supplementation, activities of immunity-related enzymes (ACP, AKP, T-AOC, SOD, CAT, GSH-Px and LZM) in plasma, liver, spleen and head kidney, and expressions of immunity-related genes (IL-1β, IFN-γ, TNF-α, and CCL-3) in liver, spleen and head kidney showed various degrees of improvement, while MDA content and Hsp70 expression level were decreased. The survival rate of tilapia increased in all the supplementation groups after Streptococcus agalactiae treatment. E. scaber extract addition changed the species composition, abundance, and diversity of intestinal microbiota in tilapia. These results demonstrate that E. scaber extract supplementation in diet can improve the growth, immunity, and disease resistance of GIFT against S. agalactiae. E. scaber extract supplementation can also change intestinal microbiota and reduce crude lipid content in dorsal muscle and liver. The above indicators show that the optimal dose of E. scaber extract for GIFT is 1 g/kg., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Serotonin (5-hydroxytryptamine) is a well-known neurotransmitter affecting emotion, behavior, and cognition. Additionally, numerous immunomodulatory functions of serotonin have been discovered in mammals. However, the regulatory role of the serotonin system in fish immunity remains unclear. In this study, various serotonergic markers in Nile tilapia ( Oreochromis niloticus ) were identified and characterized. The involvement of the serotonin system during bacterial infection was investigated. Moreover, the expression characteristics and specific functions of serotonergic markers within Nile tilapia immune cells were also assessed. Overall, 22 evolutionarily conserved serotonergic marker genes in Nile tilapia were cloned and characterized. Transcriptional levels of these molecules were most abundant in the brain, and their transcripts were induced during Streptococcus agalactiae infection. Nevertheless, few serotonergic markers exist on Nile tilapia immune cells, and no distinct immunomodulation effect was observed during an immune response. The present study lays a theoretical foundation for further investigation of the immunological mechanisms in fish as well as the evolution of the serotonin system in animals., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Li, Jiang, Zhang, Huang, Xu, Chen, Hou, Cai, Huang and Jian.)

Nile tilapia (Oreochromis niloticus) is an important food fish species that is mainly cultivated in tropical and subtropical countries. However, microbial diseases have created various difficulties for this industry. The fundamental prerequisite for tackling disease outbreak prevention and disease resistance is to know how hosts' immune responses against invading microbes are initiated. Toll-like receptors (TLRs) are vital pattern recognition receptors and play pivotal roles in the cellular innate immunity defense that is able to recognize pathogen-associated molecular patterns (PAMPs). In this study, Oreochromis niloticus TLR23 (OnTLR23) was cloned and bioinformatic analyses revealed that OnTLR23 is not an ortholog of mammalian TLR13 as previously suggested. The basal transcript level of OnTLR23 was found to be higher in the immune-related organs and was upregulated in the spleen and/or head kidney following Aeromonas hydrophila, Streptococcus agalactiae or poly I:C injections, and increased in the melanomacrophage-like tilapia head kidney (THK) cell line after LPS and zymosan stimulation. Furthermore, we demonstrated for the first time that OnTLR23 locates mainly in the intracellular region in fish cells and the constitutively active form of OnTLR23 promotes the expression of molecules related to antigen presentation, proinflammatory cytokines, antimicrobial peptides and type I interferon in THK cells. A co-immunoprecipitation assay revealed that OnTLR23 can interact with both OnMyD88 and OnTRIF, but not with OnTIRAP. A luciferase assay showed that the NF-κB activity was not elevated in the OnTLR23 overexpressed THK cells after treatment with ligand for TLR13 as well as other known purified bacterial-derived ligands of TLRs. Taken together, OnTLR23 is likely to recruit OnMyD88 and OnTRIF as adaptors to induce the expression of various effectors in melanomacrophages, but its corresponding ligand is an issue awaiting further investigation., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Substance P (SP) is a neuropeptide that involves in a wide variety of physiological and pathological events, mainly exerts its roles by neurokinin 1 receptor (NK1R), also modulates immune function. However, the roles of SP during immune response to acute bacterial infection of Nile tilapia (Oreochromis niloticus) remain unclear. In this study, the gene of SP precursor (tachykinin precursor 1, TAC1) and the gene of SP receptor (NK1R) from Nile tilapia were identified, and the roles of SP during an acute bacterial infection in a warm water environment were investigated. On-TAC1(Oreochromis niloticus-TAC1) contains conservative SP & NKA peptide sequences and On-NK1R contains seven conservative transmembrane domains. Their transcriptional levels were most abundant in brain and the On-TAC1 transcripts can be induced in the tilapia challenged with Streptococcus agalactiae. Furthermore, the experimental results revealed that On-SP could promote pyroptosis, suppress inflammation, and improve survival rate during acute bacterial infection. The present data lays a theoretical foundation to further elucidate the mechanism of SP protecting fish against pathogens., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Prenatal screening in pregnant women between 35 and 37 weeks of gestation and intrapartum antibiotic prophylaxis has successfully reduced the incidence of neonatal morbidity and mortality related to Streptococcus agalactiae. However, the contamination rates of newborns are still considerable. In traditional and folk medicines, it has been observed that garlic has been effective in treating S. agalactiae infection. The aim of this study was to isolate and identify the active compounds from garlic that have antimicrobial activity against S. agalactiae. In order to do this, SP80 (Sep-Pak 80%) obtained from crude garlic extract (CGE) was fractionated by reverse-phase ultrafast liquid chromatography with UV (RP-UFLC-UV) using a Shim-pack PREP-ODS column. All fractions obtained were tested using a microbial growth inhibition test against the S. agalactiae strain (ATCC 12386). Five clinical isolates were used to confirm the action of the fractions with antimicrobial activity, and the bacterial growth curve was determined. Identification of the antimicrobial compounds was carried out through liquid chromatography coupled with mass spectrometry (LC/MS) and nuclear magnetic resonance (NMR). The active compounds found to exhibit antimicrobial activity were Ƴ-glutamyl- S -allyl-cysteine (fraction 18), Ƴ-glutamyl-phenylalanine (fraction 20), and the two stereoisomers ( E and Z ) of ajoene (fraction 42). The MICs of these fractions were 5.41 mg/ml, 4.60 mg/ml, and 0.16 mg/ml, respectively, and they inhibited the growth of the clinical isolates tested. Antimicrobial compounds from garlic may be a promising source in the search for new drugs against S. agalactiae. IMPORTANCE Invasive disease due to group B streptococcal (GBS) infection results in a wide spectrum of clinical disease in neonates. Maternal colonization by GBS is the primary risk factor for disease. The strategy recommended by the Centers for Disease Control to reduce neonatal GBS infection is the culture-based screening of all pregnant women at 35 to 37 weeks of gestation and intrapartum antibiotic prophylaxis (IAP). However, indiscriminate use of antibiotics favors the selection and spread of resistant bacteria. The global scenario of antibacterial resistance has been of great concern for public health, and natural products can be a source of new substances to help us grapple with this problem.

The aim of this study was to investigate the role of IL-18, a member of the IL-1 family, in group B Streptococcus (GBS) infection. Both in a neonatal and adult model of GBS infection, IL-18-deficient animals were significantly more susceptible to infection than WT animals. The lack of IL18 was associated with a marked reduction in IFN-γ-levels after bacterial stimulation but did not play a significant role in the recruitment of PMN to sites of GBS infection. Collectively, our data document a fundamental function of IL-18 signaling in boosting the host immune responses against GBS infection., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Toll-like receptor 7 (TLR7) subfamily members are important pattern recognition receptors that participate in the recognition of pathogen-associated molecular patterns. In the present study, three TLR family members, OnTLR7, OnTLR8 and OnTLR9, were identified in the Nile tilapia Oreochromis niloticus. TLR7-, TLR8-and TLR9-deduced proteins have typical structural characteristics of TLRs, including Toll/interleukin-1 receptor (TIR), leucine-rich repeat (LRR) and transmembrane region (TM). OnTLR7, OnTLR8 and OnTLR9 were broadly expressed in all of the tissues tested, with the highest expression levels in the brain (TLR7) and spleen (TLR8 and TLR9). Moreover, the expression levels of OnTLR7, OnTLR8 and OnTLR9 were significantly increased in most tested tissues after Streptococcus agalactiae infection in vivo. After LPS stimulation, OnTLR7 and OnTLR9 mRNA expression levels were downregulated in the intestine and upregulated in the liver, spleen and kidney; however, OnTLR8 mRNA expression levels were upregulated in the kidney only after LPS stimulation for 5 d. After Poly I:C stimulation, OnTLR7 and OnTLR9 mRNA expression levels were upregulated in the intestine, liver, spleen and kidney, and the highest expression was found in the liver, while OnTLR8 mRNA expression levels were upregulated in the intestine, liver and kidney and downregulated in the spleen. Subcellular localization of OnTLR7, OnTLR8, and OnTLR9 in 293T cells showed that OnTLR9 was distributed in both the cytoplasm and nucleus while OnTLR8 and OnTLR7 were distributed mainly in the cytoplasm. Overexpression of OnTLR7, OnTLR8 and OnTLR9 in 293T cells had no significant effect on the activity of NF-κB, but they could significantly enhance MyD88-mediated NF-κB activity after cotransfection with MyD88. Pulldown assays showed that OnTLR7, OnTLR8, and OnTLR9 could interact with OnMyD88. Taken together, these results indicate that TLR7 subfamily genes play a role in the immune response to pathogen invasion of Nile tilapia., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The clustered regularly interspaced palindromic repeats (CRISPR)-Cas (CRISPR-associated) system is a prokaryotic defence against invading mobile genetic elements, such as bacteriophages or exogenous plasmids. Beyond this, this system has been shown to play an important role in controlling the virulence of some bacterial pathogens. Streptococcus agalactiae strain GD201008-001, a causative agent of septicemia and meningitis in tilapia, contains a single type II CRISPR-Cas system with Cas9 as a signature protein. In this study, we found that the deletion of CRISPR significantly reduced adhesion, invasion, cytotoxicity and haemolysis, and caused severely attenuated virulence in the piscine S. agalactiae strain. RNA-Seq identified 236 endogenous genes regulated by CRISPR, with 159 genes upregulated and 77 genes downregulated. The resulting change in gene transcription by CRISPR was much more pronounced than that by cas9 in this bacterium, indicating CRISPR-mediated endogenous gene regulation was mostly independently of cas9 . Subsequent studies showed that CovR/S two-component system was transcriptionally upregulated due to CRISPR deletion, which repressed the expression of the cylE gene coding for a cytolytic toxin, and thus decreased the activity of β-haemolysin/cytolysin. However, upregulation of CovR/S was not the contributor to the attenuation phenotype of ΔCRISPR. Further, we demonstrated that CRISPR is capable of repressing the expression of Toll-like receptor 2 (TLR2)-activating lipoprotein Sag0671 and thus dampens the innate immune response. This study revealed that the CRISPR system of S. agalactiae exhibited extraordinary potential capability in the regulation of endogenous transcripts, which contributes to bacterial innate immune evasion and virulence.

Although Streptococcus agalactiae periprosthetic joint infection (PJI) is not as prevalent as staphylococcal PJI, invasive S. agalactiae infection is not uncommon. Here, RNA-seq was used to perform transcriptomic analysis of S. agalactiae PJI using fluid derived from sonication of explanted arthroplasties of subjects with S. agalactiae PJI, with results compared to those of S. agalactiae strain NEM316 grown in vitro. A total of 227 genes with outlier expression were found (164 upregulated and 63 downregulated) between PJI sonicate fluid and in vitro conditions. Functional enrichment analysis showed genes involved in mobilome and inorganic ion transport and metabolism to be most enriched. Genes involved in nickel, copper, and zinc transport, were upregulated. Among known virulence factors, cyl operon genes, encoding β-hemolysin/cytolysin, were consistently highly expressed in PJI versus in vitro. The data presented provide insight into S. agalactiae PJI pathogenesis and may be a resource for identification of novel PJI therapeutics or vaccines against invasive S. agalactiae infections., (© 2021 Mayo Clinic. MicrobiologyOpen published by John Wiley & Sons Ltd.)