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Simple Summary: Plant-derived essential oils are promising preventive supplements as antibiotic alternatives in aquaculture. In this study, an essential oil blend (Phyto AquaBiotic, abbreviated as PAB) was tested in Liptopenaeus vannamei to evaluate its effect on growth improvement and mortality mitigation when infected by Vibrio parahaemolyticus (causative agent of Acute Hepatopancreatic Necrosis Disease). Shrimps were fed with two dosages of PAB for 42 days followed by a challenge against a pathogenic strain of V. parahaemolyticus. Results showed an improvement in growth performance and reduction in mortality compared to the positive control (unsupplemented with PAB and challenged against V. parahaemolyticus). Moreover, the Vibrio spp. count in the hepatopancreas of shrimps fed with 2 g/kg of this blend was markedly lower compared to that of the control. To conclude, 2 g/kg PAB contributes in reducing mortality in the context of AHPND outbreaks in whiteleg shrimp (L. vannamei). Acute Hepatopancreatic Necrosis Disease (AHPND) is a serious and emerging disease caused by a group of strains of Vibrio parahaemolyticus and affects farmed shrimp, particularly whiteleg shrimps (Liptopenaeus vannamei). The objective of this study is to assess the effect of dietary supplementation with two dosages of an essential oil mixture (Phyto AquaBiotic, abbreviated as PAB) on growth performance and mortality reduction after challenge against V. parahaemolyticus. PAB was mixed with basal diets at rates of 0, 1 and 2 g/kg and fed for 42 days. Each tank was stocked with 100 individuals with experimentation performed in triplicate. The results showed an improvement in growth performance in a dose-dependent manner, specifically regarding daily weight gain, specific growth rate and total biomass, which were significantly improved compared to control (p < 0.05). Further, PAB significantly reduced mortalities when challenged against Vibrio parahaemolyticus (p < 0.05) and decreased Vibrio spp. count in the hepatopancreas of infected shrimp. Overall, PAB was efficient in reducing mortalities in cases of disease outbreaks at a rate of 2 g/kg. [ABSTRACT FROM AUTHOR]

Toll-like receptors (TLRs) are evolutionarily conserved proteins of pattern recognition receptors (PRRs) and play a crucial role in innate immune systems recognition of conserved pathogen-related molecular samples (PAMPs). We identified and characterized TLR18 from Nile tilapia (Oreochromis niloticus), OnTLR18 , to elucidate its role in tissue expression patterns, modulation of gene expression after microbial challenge and TLR ligands, subcellular localization in fish and human cells, and the possible effectors TLR18 induces in a melanomacrophage-like cell line (tilapia head kidney (THK) cells). OnTLR18 expression was detected in all tissues examined, with the highest levels in the intestine and the lowest in the liver. OnTLR18 transcript was up-regulated in immune-related organs after bacterial and polyinosinic-polycytidylic acid (poly I:C) challenges and in the THK cells after lipopolysaccharide (LPS) stimulation. In transfected THK and human embryonic kidney (HEK) 293 cells, OnTLR18 localizes in the intracellular compartment. OnMyD88 and OnTRIF, but not OnTIRAP, were co-immunoprecipitated with OnTLR18, suggesting that the former two molecules are recruited by OnTLR18 as adaptors. The constitutively active form of OnTLR18 induced the production of pro-inflammatory cytokines, type I interferon (IFN), and antimicrobial peptides such as tumor necrosis factor α , interferon (IFN) d2.13 , tilapia piscidin (TP) 2, TP3, TP4, and hepcidin in THK cells. Our results suggest that OnTLR18 plays an important role in innate immunity through initiating nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and IFN signaling pathways via OnMyD88 and OnTRIF and induces the production of various effectors in melanomacrophages. • OnTLR18 was cloned and characterized from Nile tilapia. • The expression of OnTLR18 was induced after bacterial injection and LPS stimulation. • OnTLR18 was localized to internal cellular compartments. • OnTLR18 recruited MyD88 and TRIF as adaptors. • Overexpression of truncated OnTLR18 promotes immune-related transcription factors. [ABSTRACT FROM AUTHOR]

Myeloid differentiation factor 88 (MyD88) is an indispensable component of the toll-like receptor (TLR)- and interleukin 1 receptor-mediated signaling pathways and plays an important role in defensive immune responses. In this study, we cloned MyD88 from the Nile tilapia, Oreochromis niloticus (OnMyD88). Phylogenetic analysis showed that OnMyD88 is grouped with other teleost MyD88s and has the highest amino acid identity and similarity to fugu MyD88. The gene organization of OnMyD88 is similar to MyD88 in several other fish species, except for Atlantic salmon. Gene expression studies revealed that OnMyD88 is highly expressed in immune-related tissues, such as spleen and head kidney, and is up-regulated in spleen and head kidney tissues from fish infected by Streptococcus agalactiae. Functional studies showed that overexpressed OnMyD88 could activate NF-κB and AP-1 in human embryonic kidney (HEK) 293 and tilapia head kidney (THK) cell lines and induce the expression of proinflammatory cytokines such as IL-1β and IL-12b and chemokine IL-8 in THK cells. The result of the co-immunoprecipitation demonstrated that OnMyD88 can be recruited by OnTLR25 as its adaptor. Taken together, our study indicates that OnMyD88 plays an essential role in the innate immune responses of Nile tilapia against bacterial infection. Unlabelled Image • OnMyD88 is highly expressed in the spleen and head kidney. • OnMyD88 expression was significantly elevated by Streptococcus agalactiae infection. • OnMyD88 activated NF-κB and AP-1 reporters in HEK 293 and THK cells. • Overexpression of OnMyD88 induced the expression of pro-inflammatory cytokines. • OnMyD88 is recruited by OnTLR25 as its adaptor protein. [ABSTRACT FROM AUTHOR]