Search

Aeromonas is a ubiquitous aquatic bacteria, and it is a significant factor contributing to meat spoilage during processing and consumption. The abilities of Aeromonas salmonicida 29 and 57, which exhibit spoilage heterogeneity, to secrete protease, lipase, hemolysin, gelatinase, amylase, and lecithinase were confirmed by plate method. A total of 3948 proteins were identified by ITRAQ in extracellular secretions of A. salmonicida, and 16 proteases were found to be potentially related to spoilage ability. The complete genome sequence of A. salmonicida 57 consists of one circular chromosome and three plasmids, while A. salmonicida 29 consists of one circular chromosome, without a plasmid. Transcriptomic analysis revealed a significant number of DEGs were up-regulated in A. salmonicida 29, which were mainly enriched in metabolic pathways (e.g., amino acid metabolism, carbohydrate metabolism), indicating that A. salmonicida 29 had better potential to decompose and utilize nutrients in meat. Six protease genes (2 pepB, hap, pepA, ftsI, and pepD) were excavated by combined ITRAQ with transcriptome analysis, which potentially contribute to bacterial spoilage ability and exhibit universality among other dominant spoilage bacteria. This investigation provides new insights and evidence for elucidating metabolic and spoilage phenotypic differences and provides candidate genes and strategies for future prevention and control technology development., 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 B.V. All rights reserved.)

Here, we provide evidence that the freshwater parasitic copepod, Salmincola californiensis, acts as a vector for Aeromonas salmonicida. While investigating the effects of S. californiensis on Chinoook salmon (Oncorhynchus tshawytscha), we tangentially observed that fish infected with the copepod developed furunculosis, caused by A. salmonicida. This occurred despite being reared in pathogen-free well water in a research facility with no prior history of spontaneous infection. We further investigated the possibility of S. californiensis to serve as a vector for the bacterium via detection of fluorescently labelled A. salmonicida inside the egg sacs from copepods in which the fish hosts were experimentally infected with GFP-A449 A. salmonicida. We then evaluated copepod egg sacs that were collected from adult Chinook salmon from a freshwater hatchery with A. salmonicida infections confirmed by either culture or PCR. The bacterium was cultured on tryptic soy agar plates from 75% of the egg sacs, and 61% were positive by PCR. These three separate experiments indicate an alternative tactic of transmission in addition to direct transmission of A. salmonicida in captivity. The copepod may play an important role in transmission of the bacterium when fish are more dispersed, such as in the wild., (© 2023 John Wiley & Sons Ltd.)

Aeromonas salmonicida subsp. salmonicida ( A. salmonicida ), a Gram-negative bacterium causing furunculosis in fish, produces the siderophores acinetobactin and amonabactins in order to extract iron from its hosts. While the synthesis and transport of both systems is well understood, the regulation pathways and conditions necessary for the production of each one of these siderophores are not clear. The acinetobactin gene cluster carries a gene ( asbI ) encoding a putative sigma factor belonging to group 4 σ factors, or, the ExtraCytoplasmic Function (ECF) group. By generating a null asbI mutant, we demonstrate that AsbI is a key regulator that controls acinetobactin acquisition in A. salmonicida , since it directly regulates the expression of the outer membrane transporter gene and other genes necessary for Fe-acinetobactin transport. Furthermore, AsbI regulatory functions are interconnected with other iron-dependent regulators, such as the Fur protein, as well as with other sigma factors in a complex regulatory network.

This study reports the polyphasic identification, characterization of virulence potential, and antibiotic susceptibility of Aeromonas salmonicida subspecies salmonicida COFCAU_AS, isolated from an aquaculture system in India. The physiological, biochemical, 16s rRNA gene sequencing and PAAS PCR test identified the strain as Aeromonas salmonicida. The MIY PCR tests established the subspecies as 'salmonicida'. The in vitro tests showed the isolated bacterium as haemolytic with casein, lipid, starch, and gelatin hydrolysis activity, indicating its pathogenic attributes. It also showed the ability to produce slime and biofilm, and additionally, it possessed an A-layer surface protein. In vivo pathogenicity test was performed to determine the LD 50 dose of the bacterium in Labeo rohita fingerlings (14.42 ± 1.01 g), which was found to be 10 6.9  cells fish -1 . The bacteria-challenged fingerlings showed skin lesions, erythema at the base of the fins, dropsy, and ulcer. Almost identical clinical signs and mortalities were observed when the same LD 50 dose was injected into other Indian major carp species, L. catla and Cirrhinus mrigala. Out of the twelve virulent genes screened, the presence of nine genes viz., aerA, act, ast, alt, hlyA, vapA, exsA, fstA, and lip were detected, whereas ascV, ascC, and ela genes were absent. The A. salmonicida subsp. salmonicida COFCAU_AS was resistant to antibiotics such as penicillin G, rifampicin, ampicillin, and vancomycin while highly sensitive to amoxiclav, nalidixic acid, chloramphenicol, ciprofloxacin, and tetracycline. In summary, we have isolated a virulent A. salmonicida subsp. salmonicida from a tropical aquaculture pond which can cause significant mortality and morbidity in Indian major carp species., 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 © 2023 Elsevier Ltd. All rights reserved.)

Aeromonas salmonicida has long been known as psychrophiles since it is mainly isolated from cold water fish, and recent reports have revealed the existence of mesophilic strains isolated from warm sources. However, the genetic differences between mesophilic and psychrophilic strains remain unclear due to few complete genomes of mesophilic strain are available. In this study, six A. salmonicida (2 mesophilic and 4 psychrophilic) were genome-sequenced, and comparative analyses of 25 A. salmonicida complete genomes were conducted. The ANI values and phylogenetic analysis revealed that 25 strains formed three independent clades, which were referred as typical psychrophilic, atypical psychrophilic and mesophilic groups. Comparative genomic analysis showed that two chromosomal gene clusters, related to lateral flagella and outer membrane proteins (A-layer and T2SS proteins), and insertion sequences (ISAs4, ISAs7 and ISAs29) were unique to the psychrophilic groups, while the complete MSH type IV pili were unique to the mesophilic group, all of which may be considered as lifestyle-related factors. The results of this study not only provide new insights into the classification, lifestyle adaption and pathogenic mechanism of different strains of A. salmonicida, but also contributes to the prevention and control of disease caused by psychrophilic and mesophilic A. salmonicida., (© 2023 John Wiley & Sons Ltd.)

Furunculosis caused by Aeromonas salmonicida subsp salmonicida (Ass) is a medically and economically important bacterial disease in salmonid farms that requires therapeutic measures to prevent and control the disease. Evaluation of the effectiveness of traditional measures such as antibiotics or vaccines usually requires infecting fish experimentally. The objective of this study is to develop a method of infectious challenge of large (250-g) Rainbow trout by immersion close to natural infection conditions. We compare mortality, morbidity and anti-Ass antibody production of Rainbow trout following different bathing times (2, 4, 8 and 24 h) at a final bacterial concentration of 10 6  CFU/mL. One hundred sixty fish divided in five groups corresponding to the 4 bathing times and the non-challenged group were studied. The 24 h contact duration resulted in the infection of all fish, with a mortality rate of 53.25%. The challenged fish developed acute infection with symptoms and lesions (inappetance, altering of swimming behaviour, presence of boils) similar to those observed in furunculosis, and produced antibodies against the bacterium at 4 weeks after challenging, in contrast with the non-challenged group., Competing Interests: Declaration of competing interest None, (Copyright © 2023. Published by Elsevier Ltd.)

Worldwide, Aeromonas salmonicida is a major bacterial pathogen of fish in both marine and freshwater environments. Despite psychrophilic growth being common for this species, the number of characterized mesophilic strains is increasing. Thus, this species may serve as a model for the study of intraspecies lifestyle diversity. Although bacteria are preyed upon by protozoan predators, their interaction inside or outside the phagocytic pathway of the predator can provide several advantages to the bacteria. To correlate intraspecies diversity with predation outcome, we studied the fate of psychrophilic and mesophilic strains of A. salmonicida cocultured with the ciliate Tetrahymena pyriformis. A total of three types of outcome were observed: digestion, resistance to phagocytosis, and pathogenicity. The psychrophilic strains are fully digested by the ciliate. In contrast, the mesophilic A. salmonicida subsp. pectinolytica strain is pathogenic to the ciliate. All the other mesophilic strains display mechanisms to resist phagocytosis and/or digestion, which allow them to survive ciliate predation. In some cases, passage through the phagocytic pathway resulted in a few mesophilic A. salmonicida being packaged inside fecal pellets. This study sheds light on the great phenotypic diversity observed in the complex range of mechanisms used by A. salmonicida to confront a predator., (© The Author(s) 2022. Published by Oxford University Press on behalf of FEMS.)

Aeromonas salmonicida subspecies salmonicida, a fish pathogen, expresses various virulence factors such as an A-layer, lipases and proteases during the infection process. Not all strains of this bacterium express the same virulence factors. It is important to be able to evaluate which factors are present when characterizing strains. The A-layer and secreted lipases and proteases are usually detected by agar-based tests that require long incubation (24 h and more) and may provide ambiguous results. In the present study, protocols have been optimized to determine the presence of these virulence factors using liquid tests. For A-layer detection, the optimized method stains the positive bacteria with Coomassie Brilliant Blue. The lipases are detected by a colorimetric biochemical reaction triggered by the degradation of p-nitrophenyl dodecanoate into a yellow product detectable by spectrophotometry, if the result is positive. Both of these tests show results in less than an hour. Finally, the protease activity is measured by clarification of a medium containing milk during an overnight bacterial growth. These new protocols provide opportunities for quicker characterization of A. salmonicida subsp. salmonicida strains and, particularly, provide more precise results., (© 2021 John Wiley & Sons Ltd.)

Previously, Aeromonas sobria and A. salmonicida were identified to be the most prevalent species in salmonid farms in Korea. In this study, we evaluated the biochemical characteristics, antibiotic susceptibility and pathogenicity of A. salmonicida (3 isolates) and A. sobria (8 isolates) isolated from salmonids, and further investigated efficacy of A. salmonicida vaccine. In antibiotic susceptibility test, all of A. sobria isolates were resistant to amoxicillin and ampicillin. Six A. sobria and two A. salmonicida isolates were resistant to oxytetracycline. In challenge test, A. sobria isolates exhibited low pathogenicity in rainbow trout (Oncorhynchus mykiss) while one A. salmonicida isolate showed high pathogenicity with LD 50 of 6.4 × 10 3  CFU/fish in rainbow trout and coho salmon (Oncorhynchus kisutch). Among virulence factors, secretion apparatus (ascV and ascC) and transcription regulatory protein (exsA) of type 3 secretion system and A-layer protein genes were differentially detected in DNA or cDNA of A. salmonicida isolates, indicating their contribution to the pathogenicity. A formalin-killed vaccine of highly pathogenic A. salmonicida isolate exhibited a protective effect with relative survival rate of 81.8% and 82.9% at 8 weeks and 16 weeks post-vaccination, respectively, in challenge test., (© 2020 John Wiley & Sons Ltd.)

Sea weeds are valuable natural assets in aquaculture due to the presence of various bioactive active metabolites in them. Successful fish production and maintenance of disease free culturing systems in aquaculture with environment friendly practices is often affected by various environmental factors. Disease causing pathogens is one of the major factors. These can be controlled by the emerging technologies such as biopolymer based drug delivery systems, feed encapsulations processes and immersions of active ingredients which can possibly facilitate sustainable production by enhancing growth and immune responses in aquaculture animals. The focus of our study is on the identification of antibacterial and antioxidant compounds from two brown seaweeds, Gracilaria foliifera and Sargassum longifolium which have proven bioactive compounds. By a process of microencapsulation these bioactive compounds were encapsulated in the form of beads. Sodium caseinate and xanthan gum were mixed together to form the beads. This process helps to retain and protect the bio active ingredients from adverse reactions such as oxidation and nutritional deterioration. These microencapsulated beads were administered orally to 10 Oreochromis mossambicus the experimental fishes, with average body weight of 10-12 g and challenged against the pathogenic bacteria Aeromonas salmonicida to assess their antibacterial efficacy to control this bacterial pathogen. Microencapsulated bio active compounds were further characterized by FT-Raman, GC-MS, NMR, HPLC and SEM analysis. In this study, the effects of combined formulations of the different bioactive compounds were determined. Data obtained from the treatment of A. salmonicida infection in O. mossambicus using formulated bioactive compounds obtained from these seaweeds showed very high survival percentage in this species of fish., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The members of the genus Aeromonas are autochthonous of aquatic ecosystems and several species have been associated to septicaemia, ulcerative and haemorrhagic diseases in fish, causing significant mortality in both wild and farmed, freshwater and marine fish species. The species Aeromonas salmonicida is generally recognized as the most important fish pathogen responsible for epidemic outbreaks of furunculosis in salmonids, also being able to produce infections in other cultured fish such as turbot, halibut, sea bream or goldfish. New species, i.e. Aeromonas aquariorum, Aeromonas tecta and Aeromonas piscicola, have recently been discovered and isolated from diseased fish. The species A. piscicola and Aeromonas bestiarum are practically impossible to differentiate phenotypically and genetically (when using the 16S rRNA gene) from each other and from A. salmonicida. In the present study, two previously described PCR protocols, based on the fstA and gyrB genes, for the specific detection of A. salmonicida were re-evaluated with the type strains of all Aeromonas species and with a set of A. piscicola and A. bestiarum strains. Contrary to what had been published previously it was demonstrated that the gyrB-PCR is not specific for A. salmonicida because of cross-reactions with other Aeromonas species. However, in agreement with previous results, A. salmonicida was detected on the basis of the fstA-PCR, for which an improved protocol was proposed., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Representatives of the bacterial genus Aeromonas are some of the most notorious aquaculture pathogens associated with a range of diseases in different fish species. As the world forges toward the post-antibiotic era, alternative options for combating bacterial pathogens are needed. One such alternative option is phage biocontrol. In this study, a novel podophage—JELG-KS1—infecting Aeromonas salmonicida was retrieved from wastewater along with its host strain. The genome of the JELG-KS1 phage is a 40,505 bp dsDNA molecule with a GC% of 53.42% and 185 bp direct terminal repeats and encodes 53 predicted proteins. Genomic analysis indicates that JELG-KS1 might represent a novel genus within the subfamily Studiervirinae. Podophage JELG-KS1 is a strictly lytic phage without any identifiable virulence or AMR genes that quickly adsorbs onto the surface of host cells to initiate a 48 min long infectious cycle, resulting in the release of 71 ± 12 JELG-KS1 progeny virions per infected cell. JELG-KS1 effectively lyses its host population in vitro, even at very low multiplicities of infection. However, when challenged against a panel of Aeromonas spp. strains associated with diseases in aquaculture, JELG-KS1 shows host-specificity that is confined only to its isolation strain, immediately compromising its potential for Aeromonas spp. biocontrol in aquaculture. [ABSTRACT FROM AUTHOR]

17α-ethinylestradiol (EE2), a synthetically derived analogue of endogenous estrogen, is widely employed as a hormonal contraceptive and is recognized as a highly hazardous emerging pollutant, causing acute and chronic toxic effects on both aquatic and terrestrial organisms. It has been included in the initial Water Watch List. The aim of this study was to isolate bacteria from consortia recovered from mine sediments and acid mine drainage samples, both considered extreme environments, with the ability to degrade EE2. From the most promising consortia, isolates affiliated with the Aeromonas, Rhizobium, and Paraburkholderia genera were obtained, demonstrating the capability of growing at 50 mg/L EE2. Subsequently, these isolates were tested with 9 mg/L of EE2 as the sole carbon source. Among the isolated strains, Aeromonas salmonicida MLN-TP7 exhibited the best performance, efficiently degrading EE2 (95 ± 8%) and reaching concentrations of this compound below the limits of detection within 7 and 9 days. The final metabolites obtained are in accordance with those of the TCA cycle; this may indicate EE2 mineralization. As far as is known, Aeromonas salmonicida was isolated for the first time and identified in acid mine drainage, demonstrating its capacity to degrade EE2, making it a promising candidate for bioaugmentation and suggesting its possible applicability in low pH environments. [ABSTRACT FROM AUTHOR]

We studied the phenotypic and genomic characteristics related to the virulence and antibiotic resistance of two Aeromonas strains, which were co-isolated before an outbreak of Aeromonas veronii among diseased seabass on Agathonisi Island, Greece, in April 2015. The first strain, AG2.13.2, is a potentially pathogenic mesophilic variant of Aeromonas salmonicida, and the second, AG2.13.5, corresponds to an Aeromonas rivipollensis related to A. rivipollensis KN-Mc-11N1 with an ANI value of 97.32%. AG2.13.2 lacks the type III secretion system just like other mesophilic strains of A. salmonicida. This characteristic has been associated with lower virulence. However, the genome of AG2.13.2 contains other important virulence factors such as type II and type VI secretion systems, and toxins such as rtxA, aerolysin aer/act, and different types of hemolysins. The strain also carries several genes associated with antibiotic resistance such as the tetE efflux pump, and exhibits resistance to tetracycline, ampicillin, and oxolinic acid. In an in vivo challenge test with gilthead seabream larvae, the A. veronii bv sobria strain AG5.28.6 exhibited the highest virulence among all tested strains. Conversely, both A. salmonicida and A. rivipollensis showed minimal virulence when administered alone. Interestingly, when A. veronii bv sobria AG5.28.6 was co-administered with A. rivipollensis, the larvae survival probability increased compared to those exposed to A. veronii bv sobria AG5.28.6 alone. This finding indicates an antagonistic interaction between A. veronii bv sobria AG5.28.6 and A. rivipollensis AG2.13.5. The co-administration of A. veronii bv sobria AG5.28.6 with Aeromonas salmonicida did not yield distinct survival probabilities. Our results validate that the primary pathogen responsible for European seabass aeromoniasis is Aeromonas veronii bv sobria. [ABSTRACT FROM AUTHOR]

All the 36 known species to date of the genus Aeromonas are mesophilic except the species Aeromonas salmonicida, which includes both psychrophilic and mesophilic subspecies. For 20 years, more and more mesophilic A. salmonicida strains have been discovered. Only A. salmonicida subsp. pectinolytica has officially been classified as a mesophilic subspecies. Most mesophiles have been isolated in hot countries. We present, for the first time, the characterization of two new mesophilic isolates from Quebec (Canada). Phenotypic and genomic characterizations were carried out on these strains, isolated from dead fish from a fish farm. Isolates 19-K304 and 19-K308 are clearly mesophiles, virulent to the amoeba Dictyostelium discoideum, a surrogate host, and close to strain Y577, isolated in India. To our knowledge, this is the first time that mesophilic strains isolated from different countries are so similar. The major difference between the isolates is the presence of plasmid pY47-3, a cryptic plasmid that sometimes presents in mesophilic strains. More importantly, our extensive phylogenetic analysis reveals two well-defined clades of mesophilic strains with psychrophiles associated with one of these clades. This helps to have a better understanding of the evolution of this species and the apparition of psychrophilic subspecies. [ABSTRACT FROM AUTHOR]

Aeromonas salmonicida is a Gram‐negative bacterium that can infect a wide host range of fish populations, including salmonids and non‐salmonids as well as freshwater and marine life. Some strains of A. salmonicida cause the disease furunculosis, which can cause lethargy, intestinal inflammation, ulcers, haemorrhaging and death. The infection is spread through fish‐to‐fish contact, and the presence of infection can have devastating effects on cultivated fish populations. The purpose of this study was to explore the ability of non‐A‐layer and A‐layer A. salmonicida strains to incorporate polyunsaturated fatty acids (PUFAs) into their lipid profile and test the phenotypic effects thereof. Lipids were extracted from PUFA‐exposed cultures and analysed for lipid modification by thin‐layer chromatography and ultraperformance liquid chromatography‐mass spectrometry, showing A. salmonicida, regardless of A‐layer, capable of incorporating all seven of the PUFAs studied. Phenotypic effects were determined through the use of assays that tested for biofilm formation, membrane permeability and cyclic peptide susceptibility. Temperature‐dependent effects on biofilm formation were observed, and PUFA exposure showed significant (p <.001) increases in membrane permeability as tested by the uptake of the hydrophobic compounds crystal violet and ethidium bromide. Additionally, some PUFAs elicited modest protection and vulnerability against the membrane‐targeting cyclic peptides polymyxin B (PMB) and colistin. The diverse, strain‐specific responses to exogenous PUFAs may allude to evolved adaptive strategies that enhance survival, persistence and virulence of non‐pathogenic and pathogenic members of bacteria that oscillate between environmental and fish host niches. [ABSTRACT FROM AUTHOR]

Mining areas are characterized by extreme conditions significantly affecting the diversity of microbial communities. On the other side, mining environments can be sources of bacteria with various biotechnological applications. In this study, two bacterial isolates from mine drainage water of two tailings ponds Slovinky and Markušovce (Slovakia) were identified using the 16 S rRNA gene sequence analysis. The isolate ODK1 found in mine drainage water from Slovinky showed a 99.73% similarity to the 16 S rDNA sequence of Pseudomonas plecoglossicida strain FPC951 (NR_024662.1) deposited in the GenBank database. The phylogenetic analysis showed a high genetic variability among Pseudomonas plecoglossicida group. The isolate ODK2 found in mine drainage water from Markušovce showed a 99.93% similarity to the 16 S rDNA sequence of Aeromonas salmonicida (NR_118945.1). The phylogenetic analysis confirmed their close relationship. Today, Pseudomonas spp., as well as Aeromonas spp. represent bacteria with a high bioremediation potential. [ABSTRACT FROM AUTHOR]

Aeromonas salmonicida is a well-known cold-water pathogenic bacterium. Previously, we reported the first isolation of pathogenic A. salmonicida from diseased Epinephelus coioides, a kind of warm-water fish, and it was proved to be a putative mesophilic strain with potent pathogenicity to humans. In order to investigate the mechanisms underlying mesophilic growth ability and virulence, the transcriptome of A. salmonicida SRW-OG1 at 18, 28, and 37 °C was analyzed. The transcriptome of A. salmonicida SRW-OG1 at different temperatures showed a clear separation boundary, which might provide valuable information for the temperature adaptation and virulence regulation of A. salmonicida SRW-OG1. Interestingly, aerA and hlyA, the hemolytic genes encoding aerolysin and hemolysin, were found to be significantly up-regulated at 28 and 37 °C. Since aerolysin and hemolysin are the most well-known and -characterized virulence factors of pathogenic Aeromonas strains, the induction of aerA and hlyA was associated with the mesophilic virulence. Further study proved that the extracellular products (ECPs) purchased from A. salmonicida SRW-OG1 cultured at 28 and 37 °C showed elevated hemolytic activity and virulence than those at 18 °C. Moreover, the silence of aerA and hlyA led to significantly decreased hemolysis and virulence. Taken together, our results revealed that the mesophilic virulence of A. salmonicida SRW-OG1 might be due to the enhanced expression of aerA and hlyA induced by elevated temperatures. [ABSTRACT FROM AUTHOR]

Aeromonas salmonicida is a typical cold water bacterial pathogen that causes furunculosis in many freshwater and marine fish species worldwide. In our previous study, the pathogenic A. salmonicida (SRW-OG1) was isolated from a warm water fish, Epinephelus coioides was genomics and transcriptomics analyzed. Type II secretion system was found in the genome of A. salmonicida SRW-OG1, while the expressions of tatA, tatB, and tatC were significantly affected by temperature stress. Also, sequence alignment analysis, homology analysis and protein secondary structure function analysis showed that tatA, tatB, and tatC were highly conservative, indicating their biological significance. In this study, by constructing the mutants of tatA, tatB, and tatC, we investigated the mechanisms underlying temperature-dependent virulence regulation in mesophilic A. salmonida SRW-OG1. According to our results, tatA, tatB, and tatC mutants presented a distinct reduction in adhesion, hemolysis, biofilm formation and motility. Compared to wild-type strain, inhibition of the expression of tatA, tatB, and tatC resulted in a decrease in biofilm formation by about 23.66%, 19.63% and 40.13%, and a decrease in adhesion ability by approximately 77.69%, 80.41% and 62.14% compared with that of the wild-type strain. Furthermore, tatA, tatB, and tatC mutants also showed evidently reduced extracellular enzymatic activities, including amylase, protease, lipase, hemolysis and lecithinase. The genes affecting amylase, protease, lipase, hemolysis, and lecithinase of A. salmonicida SRW-OG1 were identified as cyoE, ahhh1, lipA, lipB, pulA, HED66_RS01350, HED66_RS19960, aspA, fabD, and gpsA, which were notably affected by temperature stress and mutant of tatA, tatB, and tatC. All above, tatA, tatB and tatC regulate the virulence of A. salmonicida SRW-OG1 by affecting biofilm formation, adhesion, and enzymatic activity of extracellular products, and are simultaneously engaged in temperature-dependent pathogenicity. [ABSTRACT FROM AUTHOR]

The importance of marine enzymes, especially protease enzymes, made us investigate the presence of these enzymes in the intestines of two fish species of the Persian Gulf (Sillago sihama and Rastrelliger kanagurta). Our investigations showed that initially 29 strains of bacteria were isolated of which 13 colonies had a specific growth in culture medium, and finally only seven strains were capable of producing a strong aura. T1/2 HR08 and S6B1 HR09 are two strains with the largest diameter of the halo around the bacteria, along with 5 other bacterial strains that were selected for more research. The results from the absorption of the supernatant by the spectrophotometer showed that the two strains T1/2 HR08 and S6B1 HR09 had the highest level of enzyme activity and were selected for identification accordingly. Also, the studies conducted with the 16S rRNA gene showed that these bacteria belonged to two genera, Kocuria and Aeromonas , from the Micrococcaceae and Aeromonadaceae families, and the highest similarity of HR08 and HR09 strains, with a similarity of 99% was shown to Kocuria rhizophila strain 8d-S5 (MN062066.1) and Aeromonas salmonicida strain SHY16- (CP038102.1), respectively. Generally, based on the results, these bacterial strains could be a good and ideal source for the production of the protease enzyme, which is used in many different industries. • The protease enzyme was extracted from the bacteria in the intestines of Sillago sihama and Rastrelliger kanagurta. • Two strains, T1/2 HR08 and S6B1 HR09, had the highest level of enzyme activity. • The utilization of fish intestines as a rich source of protease enzymes has great potential in various industries. [ABSTRACT FROM AUTHOR]

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aeromonas salmonicida (As) is a highly heterogeneous bacterial species, and strains' host specificity has been reported. Ballan wrasse (Labrus bergylta Ascanius, 1767) is susceptible to atypical As (aAs) vapA type V and type VI in Scotland and Norway. Identification of the bacterium is achieved by culture and molecular techniques; however, the available methods used to distinguish the As types are costly and time‐consuming. This paper describes the development of a PCR and a restriction enzyme assay for the detection of aAs vapA type V and type VI in ballan wrasse, respectively. Type V‐specific primers were designed on conserved regions of the vapA gene, and the restriction enzyme assay was performed on the PCR products of the hypervariable region of vapA gene for the detection of type VI isolates. Amplification product was produced for type V (254 bp) and restriction bands (368 and 254 bp) for type VI isolates only. In addition, the assays detected type V and type VI isolates in spiked water samples and type V in diagnostic tissue samples. The assays are fast, specific and cost‐effective and can be used as specific diagnostic tools for cleaner fish, to detect infectious divergence strains, and to manage and mitigate aAs disease outbreaks through vaccine development. [ABSTRACT FROM AUTHOR]

Biofilm formation causes persistent contamination of spoilage microorganisms, leading to serious economic losses in the aquatic processing industry. The antibacterial and anti-biofilm activity of ten carvacrol, cinnamaldehyde, and derivatives against two fish spoilers, Pseudomonas fluorescens and Aeromonas salmonicida, were evaluated by minimum inhibitory concentration (MIC), crystal violet staining, exopolysaccharide, adhesion, swimming, and swarming. Ten essential oils (EOs) tested showed different antibacterial activity, in which carvacrol and thymol exhibited the lowest MIC. Biofilms and exopolysaccharide production were repressed by all EOs at one-fourth MIC without affecting cell viability, as well as, adhesion. Swimming and swarming of two spoilage strains significantly decreased. Carvacrol and eugenol exerted the best anti-biofilm of P. fluorescens (42.2%) and A. salmonicida (62.9%), respectively. All tested EOs components showed that the decrease of acyl-homoserine lactone (AHL) quorum sensing (QS) signals of two strains were positively correlated with anti-biofilm based on violacein production. Molecular docking revealed that the most active EO, carvacrol, competed with C4-HSL to bind with receptor LuxR and AsaR by its hydroxyl group, resulting in the repression of biofilm formation. These results indicated that efficacy of antibiofilm for ten EOs was associated with the structure of compounds, and carvacrol exerted the strongest anti-biofilm activity mediated by QS against two spoilage strains. [ABSTRACT FROM AUTHOR]

Aeromonas is included in the Dutch Drinking Water Decree as an indicator for elevated microbial regrowth in nonchlorinated drinking water distribution systems (DWDS). The temporal and spatial diversity of Aeromonas species in 10 DWDS and their planktonic growth characteristics with regard to different carbon sources were investigated. Genotyping of the gyrB gene of isolates showed a nonsystematic temporal and spatial variable prevalence of seven different Aeromonas species in these DWDS and no correlation with the level of assimilable organic carbon determined with Pseudomonas fluorescens strain P17 and Spirillum sp. strain NOX (AOC-P17/NOX concentration) and Aeromonas concentrations. Pure cultures of these seven species showed a high affinity for low concentrations (micrograms per liter) of individual amino acids and fatty acids, compounds associated with biomass. Growth occurred at 0.5 #181;g C/literofan amino acid mixture. Growth of a mixed community of Aeromonas rivuli, Aeromonas salmonicida, Aeromonas sobria,and Aeromonas veronii in drinking water occurred in pasteurized samples; however, either no growth or decay occurred in competition with the autochthonous bacteria (nonpasteurized samples). This community also failed to grow in nonpasteurized distribution samples from a location with a clear increase in planktonic Aeromonas concentrations in the transported drinking water. For competitive planktonic growth of Aeromonas, an amino acid concentration of ≥5 µg C/liter is required. AOC-P17/NOX concentrations showed that such concentrations are not expected in Dutch drinking water. Therefore, we suspect that competitive planktonic growth is not the major cause of the observed noncompliance with the Aeromonas standard in nonchlorinated DWDS. [ABSTRACT FROM AUTHOR]

The present study was aimed at determining antimicrobial susceptibility by a CLSI standard microdilution testing protocol and detecting the resistance genes of motile Aeromonas species isolated from cultured fish. The importance of the minimum inhibitory concentrations was assessed based on statistically determined epidemiological cut‐off values calculated by normalized resistance analysis. Unfortunately, CLSI epidemiological cut‐off values are available only for Aeromonas salmonicida, and there is no further detailed data on Aeromonas isolated from aquatic animals. The antimicrobial susceptibilities of pre‐identified motile Aeromonas species to florfenicol, tetracycline and sulfamethoxazole were determined by calculating epidemiological cut‐off values with fully automated and freely available Excel spreadsheets, applying the normalized resistance interpretation (NRI) method. Furthermore, the presence of the antimicrobial resistance genes floR, tetA, tetB, tetC, tetD, tetE, tetH, sulI, sulII and sulIII was detected by PCR analysis and confirmed by sequence analysis. The presence of up to six different genes (multiple antimicrobial resistance) was determined in the Aeromonas isolates. Significance and Impact of the Study: Significance and Impact of the Study: In this study, we investigated phenotypic and genotypic antimicrobial resistance characteristics by a novel method based on epidemiological cut‐off values. This is the second comprehensive study on the antimicrobial susceptibility characteristics of Aeromonas species using NRI and epidemiological cut‐off values. The present research is related to our previous researches focussed on the identification of motile Aeromonads, their prevalence in relation to different fish lengths, seasons and regions, and covered the investigation of Lactococcus garvieae, Yersinia ruckeri, Flavobacterium spp., Enterobacter spp. and Citrobacter spp. [ABSTRACT FROM AUTHOR]

Aims: The aim of the study was to quantify the growth kinetic parameters and spoilage‐associated metabolites of an inoculated strain of Aeromonas salmonicida in pre‐rigor filleted Atlantic salmon (Salmo salar L.) stored in vacuum (VP) or modified atmosphere (MAP 60/40% CO2/N2) at 4 and 8°C. Methods and Results: The maximum growth rate of A. salmonicida in VP salmon stored at 4°C was 0·56 ± 0·04 day−1 with no detectable lag‐phase and the concentration of Aeromonas reached 8·33 log CFU per g after 10 days. The growth rates and maximum population density of Aeromonas in MAP salmon were lower but the applied atmosphere did not inhibit the growth. A selection of metabolites associated with fish spoilage were quantified using 1H nuclear magnetic resonance (NMR) spectroscopy. The concentration of trimethylamine (TMA) was significantly affected by storage time and temperature, packaging atmosphere and inoculation with A. salmonicida (General Linear Model (GLM), P < 0·001 for all factors). Conclusion: The study presents preliminary results on A. salmonicida as a potential spoilage organism in vacuum‐packaged salmon during cold storage. The combination of refrigeration and a packaging atmosphere consisting of 60/40 % CO2/N2 did not completely inhibit the growth but prevented the formation of TMA. Significance and Impact of the Study: Little information is available on the spoilage potential of Aeromonas spp. in minimally processed salmon products under different packaging conditions. The study clearly demonstrates the importance of hurdle technology and provides data to further elucidate the significance of Aeromonas spp. as a spoilage organism. [ABSTRACT FROM AUTHOR]

Aeromonas and Pseudomonas are important bacterial species involved in spoilage of refrigerated freshwater fish. In this study, 10 Aeromonas and seven Pseudomonas bacterial strains were isolated from spoiled grass carp and identified. Twelve of seventeen bacterial strains showed high potential of biofilm formation and 14 of 17 can produce extracellular protease. In order to explore the spoilage capacity of dual‐species, the sterile grass carp fillets were inoculated with mono‐ and dual‐species of Aeromonas salmonicida and Pseudomonas azotoformans strains. The results revealed significantly higher levels of the total viable count and total volatile basic nitrogen in dual‐species as compared to mono‐species from day 6. The higher contents of histamine, cadaverine and serious degradation in muscles tissue were also observed in dual‐species after 10 days of storage. Results of in vitro experiments showed that the co‐culture of A. salmonicida and P. azotoformans significantly increased the bacterial maximum growth rate, promoted the biofilm formation and improved the spoilage capacity of bacterial strains. This study has revealed that the co‐culture of Aeromonas and Pseudomonas bacterial strains accelerated spoilage process of grass carp and increased biofilm formation. It indicates that the mixed‐cultures of spoilage micro‐organisms pose a huge threat to food industry. [ABSTRACT FROM AUTHOR]

Integrons are prokaryotic genetic elements known to carry and exchange antibiotic resistance gene cassettes through a site-specific recombinase called integrase. In this work, 107 Aeromonas isolates from environmental origin, including fish, water, and sediments, were investigated for the presence of integrons. Using specific primers for Class 1, 2 and 3 integrases, only Class 1 and Class 2 integrons were detected. Detection of Class 2 integrases and their associated variable regions required two rounds of polymerase chain reaction (PCR). Sequencing of the intI2 amplicons confirmed them as integrase-derived products. Class 1 integrons were detected in 26 out of 107 isolates. PCR amplification of the variable regions associated to these integrons revealed an outstanding homogeneity, 25 of them having variable regions with an identical dfrA12-orfF-aadA2 cassette array and one integron carrying only the dfrA16 cassette. To assess clone diversity, chromosomal DNA from isolates was subjected to enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR), which discarded clonality in all instances. Class 2 integrons were surprisingly more prevalent than Class1 integrons, being detected in 60 out of 107 isolates. Forty-six of them showed a unique ERIC profile, while the remaining 14 strains displayed profiles that could be grouped in five different patterns. Cassette arrangements of all Class 2 variable regions were those described as the most prevalent (dfrA1-sat2-aadA1). A rather startling result of this work is the sensitivity to trimethoprim, streptomycin, and streptothricin of most strains, despite the presence of the cognate resistance genes. To know the integron distribution in environmental Aeromonas species, a phylogenetic reconstruction was done using rpoD/gyrB or rpoD/gyrA gene sequences. Isolates bearing these elements corresponded to Aeromonas hydrophila, Aeromonas veronii, Aeromonas salmonicida, Aeromonas dhakensis, Aeromonas sanarellii, Aeromonas taiwanensis, Aeromonas media, Aeromonas caviae, Aeromonas jandaei, and Aeromonas sp. This work revealed an unusual high incidence of Class 2 integrons and a low variability of cassette arrangements in environmental Aeromonas species. [ABSTRACT FROM AUTHOR]

Aims: The object of this study was to identify potential health concerns of the Aeromons spp. isolated from marketed Pacific abalone (Haliotis discus hannai) with respect to their virulence and antimicrobial resistance patterns. Methods and Results: We identified 29 strains of aeromonads consisting of five species; Aeromonas hydrophila (n = 9), Aeromonas enteropelogenes (n = 14), Aeromonas veronii (n = 3), Aeromonas salmonicida (n = 2) and Aeromonas sobria (n = 1), by employing series of biochemical tests and gene sequencing. In the phenotypic virulence assays, all isolates showed gelatinase and caseinase activities, while lipase formation (69%), phospholipase production (90%), DNase formation (82%), slime production (49%) and haemolysis activity (α = 18% and β = 82%) were also detected among isolates. Prevalence of virulence genes; aerA (100%), fla (66%), ahyB (73%), act (52%), alt (42%), ast (35%), ser (52%), gcat (69%), ascV (43%), hlyA (83%), lip (52%) and exu (59%) were detected by PCR assays. In disc diffusion test, 100% resistance was detected against ampicillin while cephalothin, rifampicin, oxytetracycline, colistine sulphate, nalidixic acid and piperaciliin were resisted by 86, 73, 42, 35, 28, 20 and 20% of the isolates respectively. Thirteen (45%) of the isolates showed multiple antimicrobial resistance (MAR) indices ≥ 0·2. Conclusions: Our findings suggest that the potential health risk posed by the abalone‐borne Aeromonas spp. should not be underestimated. Significance and Impact of the Study: This is the first time to evaluate possible public health risks upon consumption of abalone harbored Aeromonas spp. and also to isolate potential pathogenic and multidrug‐resistant Aeromonas spp. from Pacific abalone in Korea. [ABSTRACT FROM AUTHOR]

From 2011, lamprey (Geotria australis) populations in Southland, New Zealand have been affected by reddening along the length of the body and increased mortalities, termed lamprey reddening syndrome (LRS). Molecular testing, bacteriology, histopathology and epidemiology were used to determine if an infectious agent was present and to increase the understanding of this syndrome. An atypical Aeromonas salmonicida was detected from affected lamprey in 2011. This organism has not previously been reported from New Zealand. Investigative molecular testing indicated the organism was an uncharacterised, unculturable, atypical A. salmonicida and a likely incidental finding. Histopathology did not indicate an infectious process was involved, but suggested the reddening may be due to blunt trauma. Epidemiological investigation found the Mokoreta River had a significantly higher prevalence of LRS than others in the Southland region, but there was no clear reason why. To date, no infectious aetiology for this syndrome has been identified. [ABSTRACT FROM AUTHOR]

In non‐salmonid fish, Aeromonas salmonicidacan cause local infections with severe skin ulcerations, known as atypical furunculosis. In this study, we present a systemic infection by a virulent A. salmonicidain European perch (Perca fluviatilis).This infection was diagnosed in a Swiss warm water recirculation aquaculture system. The isolate of A.  salmonicida encodes a type three secretion system (TTSS) most likely located on a plasmid similar to pAsa5/pASvirA, which is known to specify one of the main virulence attributes of the species A. salmonicida. However, the genes specifying the TTSS of the perch isolate show a higher temperature tolerance than strains isolated from cold‐water fish. The function of the TTSS in virulence was verified in a cytotoxicity test using bluegill fry and epithelioma papulosum cyprinid cells. [ABSTRACT FROM AUTHOR]

Abstract Recently, the rarely reported tet (31) tetracycline resistance determinant was commonly found in Aeromonas salmonicida , Gallibacterium anatis , and Oblitimonas alkaliphila isolated from farming animals and related environment. However, its distribution in other bacteria and potential molecular dissemination mechanism in environment are still unknown. The purpose of this study was to investigate the potential mechanism underlying dissemination of tet (31) by analysing the tet (31)-carrying fragments in A. caviae strains isolated from an aerobic biofilm reactor treating oxytetracycline bearing wastewater. Twenty-three A. caviae strains were screened for the tet (31) gene by polymerase chain reaction (PCR). Three strains (two harbouring tet (31), one not) were subjected to whole genome sequencing using the PacBio RSII platform. Seventeen A. caviae strains carried the tet (31) gene and exhibited high resistance levels to oxytetracycline with minimum inhibitory concentrations (MICs) ranging from 256 to 512 mg/L. tet (31) was comprised of the transposon Tn 6432 on the chromosome of A. caviae , and Tn 6432 was also found in 15 additional tet (31)-positive A. caviae isolates by PCR. More important, Tn 6432 was located on an integrative conjugative element (ICE)-like element, which could mediate the dissemination of the tet (31)-carrying transposon Tn 6432 between bacteria. Comparative analysis demonstrated that Tn 6432 homologs with the structure IS CR2 - ∆phzF - tetR (31)- tet (31)- ∆glmM - sul2 were also carried by A. salmonicida , G. anatis , and O. alkaliphila , suggesting that this transposon can be transferred between species and even genera. This work provides the first report on the identification of the tet (31) gene in A. caviae , and will be helpful in exploring the dissemination mechanisms of tet (31) in water environment. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Aeromonas spp. are closely associated with food spoilage, and often enter the food chain through cross-contamination during processing from biofilms on food-contacted surfaces. The attachment abilities of two high-spoilage Aeromonas salmonicida isolates were compared. The sensitivities of these isolates in biofilm to four disinfectants, namely sodium hypochlorite, chlorine dioxide, acidic electrolyzed water (AEW) and neutral electrolyzed water (NEW), were assayed. The results indicated that isolate 1425 showed higher attachment ability as compared to isolate 1435 at initial attachment (30 min) under a short-term attachment scenario (5 h), reaching more than 5 log CFU/cm 2 . Under a long-term attachment scenario (7 days), isolate 1425 formed a mature biofilm after 5 days of incubation, with the highest observed cell numbers of nearly 9 log CFU/cm 2 . The dynamics of biofilm formation of isolate 1435 were relatively stable, with cell population ranging from 6.25 to 7 log CFU/cm 2 . The composition of the extracellular polymeric substances and the morphology of the mature biofilm were identified by Attenuated Total Reflection Fourier Transform Infrared spectroscopy (ATR-FTIR) and Confocal Laser Scanning Microscopy (CLSM). The mature biofilm formed by isolate 1425 showed more resistance to tested disinfectants than that of isolate 1435. Sodium hypochlorite (200 mg/L) and AEW (40 mg/L) showed greater lethal effects than the other disinfectants. Moreover, 40 mg/L of AEW was as effective as 200 mg/L of sodium hypochlorite. These findings indicated that the biofilm formed by microorganisms associated with food spoilage and safety could not be ignored during food processing and that AEW may be a promising alternative to sodium hypochlorite for the elimination of such biofilms. [ABSTRACT FROM AUTHOR]

Background: Due to the predominant usage of short-read sequencing to date, most bacterial genome sequences reported in the last years remain at the draft level. This precludes certain types of analyses, such as the in-depth analysis of genome plasticity. Results: Here we report the finalized genome sequence of the environmental strain Aeromonas salmonicida subsp. pectinolytica 34mel, for which only a draft genome with 253 contigs is currently available. Successful completion of the transposon-rich genome critically depended on the PacBio long read sequencing technology. Using finalized genome sequences of A. salmonicida subsp. pectinolytica and other Aeromonads, we report the detailed analysis of the transposon composition of these bacterial species. Mobilome evolution is exemplified by a complex transposon, which has shifted from pathogenicity-related to environmental-related gene content in A. salmonicida subsp. pectinolytica 34mel. Conclusion: Obtaining the complete, circular genome of A. salmonicida subsp. pectinolytica allowed us to perform an in-depth analysis of its mobilome. We demonstrate the mobilome-dependent evolution of this strain's genetic profile from pathogenic to environmental [ABSTRACT FROM AUTHOR]

Precise deletion of genes related to virulence can be used as a strategy to produce attenuated bacterial vaccines. Here, we study the deletion of the cyclic-3′,5′-adenosine monophosphate ( cAMP) receptor protein (Crp) in Aeromonas salmonicida, the aetiologic agent of furunculosis in marine and freshwater fish. The Crp protein is a conserved global regulator, controlling physiology processes, like sugar utilization. Deletion of the crp gene has been utilized in live attenuated vaccines for mammals, birds and warm water fish. Here, we characterized the crp gene and reported the effect of a crp deletion in A. salmonicida virulent and non-virulent isolates. We found that A. salmonicida Δ crp was not able to utilize maltose and other sugars, and its generation time was similar to the wild type. A. salmonicida ∆ crp showed a higher ability of cell invasion compared to the wild type. Fish challenges showed that A. salmonicida ∆ crp is ~6 times attenuated in Oncorhynchus mykiss and conferred protective immunity against the intraperitoneal challenge with A. salmonicida wild type. We concluded that deletion of A. salmonicida crp influences sugar utilization, cell invasion and virulence. Deletion of crp in A. salmonicida could be considered as part of an effective strategy to develop immersion live attenuated vaccines against furunculosis. [ABSTRACT FROM AUTHOR]

When challenged with atypical Aeromonas salmonicida subsp . salmonicida, exposure of the common carp ( Cyprinus carpio L.) to different humic-rich compounds resulted in a significant reduction in infection rates. Specifically, in fish exposed to (i) humic-rich water and sludge from a recirculating system, (ii) a synthetic humic acid, and (iii) a Leonardite-derived humic-rich extract, infection rates were reduced to 14.9%, 17.0% and 18.8%, respectively, as compared to a 46.8% infection rate in the control treatment. An additional set of experiments was performed to examine the effect of humic-rich components on the growth of the bacterial pathogen. Liquid culture medium supplemented with either humic-rich water from the recirculating system, the synthetic humic acid or the Leonardite humic-rich extract resulted in a growth reduction of 41.1%, 45.2% and 61.6%, respectively, as compared to the growth of the Aeromonas strain in medium devoid of humic substances. Finally, in a third set of experiments it was found that while the innate immune system of the carps was not affected by their exposure to humic-rich substances, their acquired immune system was affected. Fish, immunized against bovine serum albumin, displayed elevated antibody titres as compared to immunized carps which were not exposed to the various sources of humic substances. [ABSTRACT FROM AUTHOR]