Atchariya Suwannasang, Naraid Suanyuk, Akkarawit Issaro, Wutiporn Phromkunthong, Chutima Tantikitti, Toshiaki Itami, and Terutoyo Yoshida

DOI: 10.14456/sjst-psu.2017.47

pp. 429 - 437

Abstract

The protective efficacy of formalin-killed Streptococcus agalactiae (Group B Streptococcus, GBS) serotype Ia (GBS-Ia)
and III (GBS-III) vaccines were assessed in Nile tilapia (Oreochromis niloticus). The fish with an average weight of 34.45±
0.08 g were immunized by intraperitoneal (i.p.) injection with 4 different formalin-killed vaccines prepared from GBS-Ia
(1×10¹⁰ CFU/mL), GBS-III (1×10¹⁰ CFU/mL), and combined GBS-Ia and GBS-III in an equal volume at final concentrations
1×10¹⁰ CFU/mL and 2×10¹⁰ CFU/mL in comparison with the non-immunized control group. At 2 and 4 weeks post vaccination,
no significant differences were observed (p>0.05) among treatments in growth performance or haemato-immunological
parameters, except the increased red blood cell at 2 weeks. Significantly increased antibody titers (p<0.05) against GBS-Ia
and GBS-III antigens were noted in the groups immunized with homologous GBS vaccines, whereas the group reacted with
heterologous GBS antigen showed less antibody titer as compared with the control group. The vaccination experiment
indicated that i.p. injection of Nile tilapia with formalin-killed cells prepared from GBS-Ia or GBS-III provides significant
protection, with relative percent survival (RPS) value of 52.17 to 71.42%, against a challenge with the homologous serotype
isolate, whereas the RPS in fish challenged with a heterologous serotype isolate varied from 20.00 to 53.57%. These results
suggested that vaccines from either GBS-Ia or GBS-III have insufficient cross-protective efficacy against the other serotypes.
However, a mixed vaccine produced from both GBS serotypes Ia and III provided significant protection with 65.00 to 95.66%
RPS which could be an excellent vaccine to protect fish against streptococcosis caused by both GBS serotypes Ia and III.