Lancefield group C Streptococcus dysgalactiae infection responsible for fish mortalities in Japan

Abstract

A Lancefield serological group C Streptococcus sp. was isolated from cultured amberjack, Seriola dumerili Risso, and yellowtail, Seriola quinqueradiata Temminck and Schlegel, immunized with Lactococcus garvieae commercial vaccines in Japan. The isolated bacteria were Gram-positive cocci, auto-aggregating in saline, morphologically long chains in growth medium, catalase negative and alpha-haemolytic on blood agar. An almost complete gene sequence of the 16S rDNA of two isolates was determined and compared with that of bacterial strains in the database. The isolates were identified as Streptococcus dysgalactiae based on the results of the 16S rDNA sequence, the bacteriological properties and the Lancefield serological grouping. Oligonucleotide primers specifically designed for the 16S-23S rDNA intergenic spacer region of S. dysgalactiae amplified a gene from all the fish isolates, as well as the type strains alpha-haemolytic S. dysgalactiae subsp. dysgalactiae ATCC430738 and beta-haemolytic S. dysgalactiae subsp. equisimilis ATCC35666, but not those of S. equi ATCC33398, Lactococcus garvieae ATCC43921 and L. garvieae KG9408. The severe necrotic lesions of the caudal peduncle seen in experimentally infected fish were similar to those seen in naturally infected fish.

Isolation and characterization of Streptococcus dysgalactiae from diseased Acipenser schrenckii

“…Three-fifth and four-fifth healthy sturgeons died after being challenged with the dosage of 4 × 10 8 CFU of sturgeon's isolates and LD50 value of one representative isolate for crucian carps was 2.45 × 10 8 -5.54 × 10 8 CFU even after passage through them three times. So it could be concluded that bacterial isolates from sturgeon really had virulence but their virulence was relatively low, which was in consistency with the reports of Nomoto et al (2004) and Shen et al (2005). As to the incidence of long time spanning on the spot, the reasons we suggested included breeding with high density, lack of disinfection treatment of fish food stuff and water exchange with outer-layered water of farming networks apart from conditional pathogenicity of S. dysgalactiae.…”

“…And so was the partial tuf gene sequence under the number EU595708. Similarities between our 16S rDNA sequence and those (AB159678 and AB102730) from amberjack or yellowtail (Nomoto et al, 2004) as well as S. dysgalactiae strain ATCC43078 (AB002485) were 99.7%, 99.7% and 99.3% respectively while similarities between our tuf gene sequence and those (AF274743 and AY582542) of S. pyogenes ATCC19615 and S. dysgalactiae ATCC43078 were both 99.5%, simultaneously with the 153-bp sequence between the two Streptococcus-specific primers being fully identical.…”

“…Warm water (usually above 25°C) made incidence of diseases increased (Nomoto et al, 2004); so the range 24-27°C was taken for challenge temperature. When challenged with dosage of 4 × 10 8 CFU, 80% of grass carps died; and LD50 value for crucian carps was in the range of 2.45 × 10 8 -5.54 × 10 8 CFU.…”

“…Among these species, S. dysgalactiae has been reported as fish pathogen with low frequency while S. iniae reported with high frequency. To the best of our knowledge, infections of S. dysgalactiae happened only on amberjack, Seriola dumerili (Risso), yellowtail, Seriola quinqueradiata (Temminck and Schlegel) (Nomoto et al, 2004), seal, Phoca vitulina and Halichoerus grypus (Vossen et al, 2004), and golden pomfret, Trachinotus ovatus (Zhou et al, 2007).…”

“…The streptococcal infections usually cause high mortality and last a long period of time (Yanong and Francis-Floyd, 2006). To date, streptococcal pathogens of fish comprise Streptococcus iniae, Streptococcus milleri (Yanong and Francis-Floyd, 2006), Streptococcus parauberis (Doménech et al, 1996), Streptococcus agalactiae (Evans et al, 2002), Streptococcus ictaluri (Shewmaker et al, 2007), and Streptococcus dysgalactiae (Nomoto et al, 2004;Vossen et al, 2004;Zhou et al, 2007). Among these species, S. dysgalactiae has been reported as fish pathogen with low frequency while S. iniae reported with high frequency.…”