Cloning and expression of a surface immunogenic protein in Streptococcus dysgalactiae isolated from fish and its application in enzyme‐linked immunosorbent assays to diagnose S. dysgalactiae infections in fish

Abstract

Lancefield group C Streptococcus dysgalactiae (GCSD) causes severe necrotic lesions in the caudal peduncle in the genus Seriola farmed in Japan. To develop a sero-diagnostic method for GCSD infection in farmed fish, we attempted to identify a surface immunogenic protein that induces an antibody after infection with GCSD by immunoblot analysis using sera collected from infected fish. A protein obtained from sodium dodecyl sulfate (SDS) extracts of GCSD was identified as S. dysgalactiae surface immunogenic protein (Sd-Sip). Sd-Sip exhibited more than 94% homology with a surface antigen or a hypothetical protein from S. dysgalactiae mammalian isolates at the nucleotide sequence level. Expression of the recombinant Sd-Sip (rSd-Sip) was confirmed by immunoblot analysis, that is, its reactivity to GCSD-infected sera. Antibody detection ELISA using rSd-Sip and their usefulness for diagnosis of GCSD infection were examined. GCSD-infected sera collected from farmed amberjack, Seriola dumerili (Risso), showed strong reaction with immobilized rSd-Sip. Meanwhile, sera immunized by other pathogenic bacteria of fish were showed ELISA values similar to those of non-infected sera. These results of this study suggest that the antibody detection ELISA using rSd-Sip is an effective diagnostic method for GCSD infection in fish.

Isolation, identification and character analysis of Streptococcus dysgalactiae from Megalobrama terminalis

“…S. dysgalactiae infection was first reported in Japan in 2002 (Nomoto et al, ). This species is an emerging pathogen that can cause severe disease in many farmed fish species throughout the world, including amberjack ( Seriola dumerili ), yellowtail ( Seriola quinqueradiata ) and king fish ( Seriola lalandi ) in Japan (Nishiki, Minami, Itami, & Yoshida, ; Nishiki et al, ; Nomoto et al, ); pompano ( Trachinotus blochii ) and white‐spotted snapper ( Lutjanus stellatus ) in Malaysia (Abdelsalam, Asheg, & Eissa, ; Abdelsalam, Chen, et al, ); hybrid red tilapia ( Oreochromis sp.) in Indonesia (Abdelsalam, Chen, et al, ); Nile tilapia ( Oreochromis niloticus ) in Brazil (Netto, Leal, & Figueiredo, ); grey mullet ( Mugil cephalus ), cobia ( Rachycentron canadum ) and soiny mullet ( Liza haematocheila ) in Taiwan (Abdelsalam, Chen, et al, ; Tsai, Wang, Yoshida, & Chen, ); and golden pompano ( Tranchinotus ovatus ) (Cai et al, ) and different species of cultured sturgeon ( Acipenser baerii , Acipenser schrenckii and Acipenser gueldenstaedti ) in China (Pan et al, ; Yang & Li, ; Yang et al, ).…”