Preliminary Report: Development of Fish Formalin-inactivated Streptococcus iniae Vaccine

TM Huang , SH Cheng, CH Wu, and C Tu

Animal Health Research Institute, Council of Agriculture, Executive Yuan

Abstract

Streptococcosis is an important fish disease causing mortality and economic losses in
the fishing industry. Prevention and control of fish streptococcosis includes administration of
antimicrobials or vaccines. The objective of the present study was to develop a formalin-inactivated
Streptococcus iniae vaccine. The seed strain 99v2942 was cultured with brain heart infusion (BHI)
broth at 25℃, shaken at 150 rpm for 24 hours to achieve log phase growth with a concentration of
1x109 CFU/ml. Incubation with 0.5% formalin at 4℃ and 150 rpm-shaking for 48 hours inactivated
the S. iniae culture. A batch of formalin-inactivated vaccine was produced according to previously
described conditions. Safety and efficacy of the inactivated vaccine was tested with sea bass and
giant grouper. No adverse effects were observed in vaccinated groups during two-week
postimmunization. Relative percent survival (RPS) of challenge by seed strain was equal or higher
than 80%. The results of this study indicated that immunization with the formalin-inactivated S.
iniae vaccine could produce a high level of immune protection against S. iniae.

Keyword: fish streptococcosis, inactivated vaccine, efficacy.