Dietary supplementation of Pediococcus pentosaceus enhances innate immunity, physiological health and resistance to Vibrio anguillarum in orange-spotted grouper (Epinephelus coioides)

• Lactic acid in LAB4012 metabolites inhibited the growth of Vibrio anguillarum.
• LAB4012-feeding protected groupers from V. anguillarum infection.
• LAB4012-feeding improved growth rate and blood cell counts in groupers.
• LAB4012-feeding regulated immune gene expression.
• LAB4012-feeding enhanced phagocytosis of head-kidney phagocytes in groupers.

Groupers (Epinephelus spp.) are economically important fish species in Southeast Asian aquaculture. Vibriosis caused by Vibro spp. is one of the severe bacterial diseases that devastate the grouper aquaculture industry. Probiotics have been reported to show the potential to enhance fish immunity and to antagonize pathogens. In our previous study, a lactic acid bacterium Pediococcus pentosaceus strain 4012 (LAB4012), isolated from cobia intestine, protects cobia from photobacteriosis after a 2-week feeding. In this study, we examined the potential of LAB4012 to be a probiotic for the orange-spotted grouper through feeding, thus to guard against vibriosis. In vitro, LAB4012 culture supernatant with low pH suppressed the growth of Vibrio anguillarum, and lactic acid in the metabolite of LAB4012 appeared to be the major factor to the growth inhibition of V. anguillarum. In vivo, the challenge test showed that the cumulative mortality of the LAB4012-fed groupers was significantly lower than that of the control fish after V. anguillarum infection. Supplementation of LAB4012 in commercial diet not only enhanced the growth rate and erythrocyte numbers of the groupers, but also regulated the gene expression of the pro-/anti-inflammatory cytokines. One day post-infection of V. anguillarum, the leukocyte numbers in the peripheral blood and the phagocytic activity of the head-kidney phagocytes in the LAB4012-fed groupers were found significantly increased, when compared with those without LAB4012-feeding. These results suggested that LAB4012 can be a dietary probiotic for groupers in modulating the immunity and protecting the groupers from V. anguillarum infection.