STREPTOCOCCOSIS VACCINE BASED ON SEROTYPING OF Streptococcus agalactiae ISOLATES FROM TILAPIA CULTURE SYSTEM IN THAILAND

Nontawith Areechon*, Korntip Kannika, Tarntip Wongwaipairote, Prapansak Srisapoome, Ikuo Hirono, Hidehiro Kondo, and Sasimanas Unajak
 
 Department of Aquaculture, Faculty of Fisheries
 Kasetsart University, Bangkok 10900, Thailand
 ffisnwa@ku.ac.th

We have collected 124 isolates of Streptococcus agalactiae from tilapia pond and cage culture from all regions in Thailand. Serotyping characterization of all isolates was performed by capsular polysaccharide (cps) gene cluster PCR analysis. We found only 2 serotypes, Ia and III which were distributed quite evenly in the country. The virulence test in Nile tilapia showed the higher virulence of serotype III (Fig 1). Formalin killed vaccine from both serotypes were prepared to determine the efficacy and cross immunity by monitoring the antibody titer and resistance to S. agalactiae.

Vaccine of single serotype and mixed serotype did show significantly good protection against S. agalactiae challenge (P<0.05). Cross immunity between serotypes has been detected from both antibody titer (Fig 2) and resistance against S. agalactiae (RPS) (Fig 3). Mixed-serotype vaccine appeared to show good protection against both serotypes. From this result, we have developed the bivalent vaccine from serotype Ia and III to be used as an universal vaccine for tilapia culture in Thailand.