Efficacy of inactive bivalent and trivalent Streptococcus agalactiae bacteria (biotype 1 & 2) vaccines on tilapia, Oreochromis niloticus

Streptococcosis is a significant fish disease impacting tilapia culture in Indonesia, causing losses estimated up to IDR 15.0 billion annually. This study aims to assess the efficacy of bivalent and trivalent vaccines containing Streptococcus agalactiae bacteria on tilapia. The formula of the bivalent vaccine contains 75% of S01-196-16 and 25% of N14G isolates (v/v). Trivalent vaccine contains 30%, 35%, and 35% of N14G, NP1050, and SG01-16 isolates (v/v), respectively. A challenge test assessed the efficacy of the vaccines, and it was carried out at 30, 90, and 150 days post-vaccination by artificially infection at LD60. Selected bacteria isolate to be appointed in the challenge test are N14G (biotype 2) and S01-196-16 (biotype 1). Relative Percentage of Survival (RPS) was used as the main indicator of vaccine efficacy. The results revealed that the highest RPS of a bivalent vaccine against S. agalactiae (S01-196-16) was achieved at the first challenge (61.84%), and trivalent vaccine against S. agalactiae (N14G) and S. agalactiae (S01-196-16) was achieved at the first challenge (61.53% and 76.20%, respectively). Bivalent and trivalent S. agalactiae bacteria vaccines are promising “tools” to control streptococcosis on tilapia