Efficacy of a Streptococcus iniae modified bacterin delivered using OraljectTM technology in Nile tilapia (Oreochromis niloticus)

This study evaluated the potential to orally deliver a previously developed Streptococcus iniae vaccine in tilapia using OraljectTM technology. This technology was developed to administer bioactive compounds to monogastric animals, and has been shown to be effective for delivery of a variety of antigens in numerous fish species. Two different formulations containing two doses of vaccine (four treatments) were fed to tilapia (4 tanks of 25 fish each) for 1 (Oralject-1 and Oralject-2 each containing 2×10 cells/g of feed) day (am and pm to satiation) or 5 (Oralject-1 and -2 each containing 2×10 cells/g of feed) days (once daily to satiation). The incorporated vaccine was a patented lyophilized modified bacterin (US Patent No. 6,379,677 B1). A positive control treatment [intraperitoneally (i.p.) injected S. iniae vaccine] and a negative control treatment (i.p. injection of tryptic soy broth, TSB) were included. Mean percent intake indicated that tilapia fed for 1 day (twice to satiation) the Oralject-1 consumed significantly (Pb0.05) more feed than fish fed Oralject-2 (4.05% vs. 3.21%, respectively). Fish fed for 5 days either commercial feed or Oralject-1 or -2 also showed differences in feed intake; on most days, fish consumed significantly less (Pb0.05) Oralject-2 (∼1%) than the commercial diet or Oralject-1 (∼2.5%). Tilapia were challenged 23 days post-vaccination by i.p. injection of 1×10 CFU S. iniae/fish. Mean percent mortality was 47.5 (±7.5) in the TSB-immunized challenged tilapia and was significantly higher (Pb0.001) than in all immunized groups. No mortality occurred in the i.p.-vaccinated tilapia. Mortality ranged from 17.5 to 31.25 in the OraljectTM treatments. Relative percent survival was 100% in the i.p.-vaccinated tilapia and 63.1% in the most effective Oralject-vaccine-treated group. The results suggest that oral delivery of the lyophilized S. iniae vaccine using OraljectTM technology provided protection against streptococcal disease. These data validate an initial proof-of-principle for oral vaccination of tilapia using S. iniae in the OraljectTM system. Published by Elsevier B.V.