Protection of Penaeus monodon against white spot syndrome by continuous oral administration of a low concentration of Bacillus subtilis spores expressing the VP28 antigen

In this study, Bacillus subtilis spores expressing a chimeric protein, CotB-VP28, were used as a probiotic vaccine to protect black tiger shrimps (Penaeus monodon) against white spot syndrome virus (WSSV) infection. Oral administration of pellets coated with CotB-VP28 spores (at ≥1 × 109 CFU per g pellet) to shrimps induced immune-relating phenoloxydase activity (PO) in shrimps after 14 days of feeding (prior challenge) and at day 3 post challenge (1·26 and 1·70 fold increase respectively). A 75% protection rate was obtained by continuous feeding of the spore-coated pellets at ≥1 × 109 CFU per g for 14 days prior to WSSV challenge and during all the postchallenge period. Even when the amount of CotB-VP28 spores in feed pellets was reduced down to ≥5 × 107 CFU per g and ≥1 × 106 CFU per g, relatively high protection rates of 70 and 67·5%, respectively, were still obtained. By contrast, feeding pellets without spores (untreated group) and with naked spores (PY79 group) at ≥1 × 109 CFU per g could not protect shrimps against WSSV. These data suggest that supplementation of CotB-VP28 spores at low dose of ≥1 × 106 CFU per g could be effective as a prophylactic treatment of WSS for black tiger shrimps. Significance and Impact of the Study This study reports the protective efficacy of Bacillus subtilis CotB-VP28 spores on black tiger shrimps (Penaeus monodon) against white spot syndrome virus infection. Oral administration of pellets coated with CotB-VP28 spores (≥1 × 109 CFU per g) conferred 75% protection after white spot syndrome virus challenge. Even after reducing CotB-VP28 spores in feed pellets to ≥1 × 106 CFU per g, 67·5% protections was still obtained. These data indicate that supplementation of CotB-VP28 spores at a low dose of ≥1 × 106 CFU per g could be effective in prophylaxis against white spot syndrome in black tiger shrimps.