Isolation,identification and characterization of Streptococcus suis serotype 7

Seventeen isolates of Streptococcus suis serotype 7 from the diseased pigs with "hyperpyrexia syndrome" in Hubei province,China,were characterized by automatic biochemical identification,PCR typing,antimicrobial susceptibility testing,PCR test of virulence gene,animal test assay and pathobiology.The results of automatic biochemistry identification indicated that all isolates belonged to serotype 2,but serotype 7 by PCR typing.Sequence homology of all strains was 100% with previously reported.The distribution of virulence gene of 17 serotype 7 strains showed that mrp+(0.0%),epf+(11.8%),sly+orf2+(17.6%),fbps+(29.4%),gdh+(100.0%).Antimicrobial susceptibility of all strains to 28 antimicrobial agents varied,but 15(88.2%) strains were resistance to amoxicillin,compound amoxicillin respectively and 17(100%) strains were susceptible to erythromycin.Result of mouse virulence test showed that virulence of strain HB6,HB8,HB9 was higher than others.In histopathology,congestion and hemorrhage of main organs were obvious in diseased pigs and infection mice.In conclusion,S.suis serotype 7 had existed in Hubei province and there was polyinfection of serotype 7 in pigs with "hyperpyrexia syndrome" whose mainly pathogen was PRRSV.