Dietary supplementation with Pediococcus pentosaceus promotes resistance to betanodavirus and ranavirus in giant groupers

Groupers are frequently infected with nervous necrosis virus (NNV) and grouper iridovirus (GIV) in Asian aquaculture. In this study, Pediococcus pentosaceus strain 4012 (LAB4012) was administered to giant groupers to evaluate its potential in protecting the fish from NNV and GIV. The results revealed that LAB4012 supplementation for 1–4 weeks did not affect the growth rate of groupers. NNV and GIV challenge tests demonstrated a decrease in the cumulative mortality of groupers fed with LAB4012. After the groupers were fed with LAB4012 for 4 weeks, the Mx gene expression levels in their head kidneys and the gene expression levels of tumor necrosis factor (TNF)-α and C3 in their intestines were upregulated. We also observed an increase in the phagocytic activity and respiratory burst of peripheral blood leukocytes in the LAB4012-fed groupers. LAB4012 safely passed through the digestive tract and survived in the groupers' intestines. Neither LAB4012 nor its culture supernatant (CS4012) induced Mx gene expression in GF-3 cells. However, the CS4012 neutralized the GIV, blocked the GIV receptors responsible for viral attachment, and suppressed NNV replication in vitro. In conclusion, LAB4012 has potential for application in grouper aquaculture for preventing viral diseases caused by NNV and GIV.