PCR detection and PFGE genotype analyses of streptococcal clinical isolates from tilapia in Guangxi

To acquire the data upon the clinical dominant strains of tilapia Streptococcus spp.and their genotype variations in Guangxi province,a total of 77 clinical Streptococcus spp.strains collected from the epidemic areas of Guangxi from 2006 to 2012 were identified by species-specific PCR.Among them,37 strains collected from 2006 to 2011 were genotyped by the pulse field gel electrophoresis(PFGE)method.As a result,57 out of 77 strains were identified as Streptococcus agalactiae,and the rest were determined as S.iniae by PCR identification process.As is shown,the dominant strains from 2006 to 2007 were S.iniae,accounted for 94.7%(18/19),only 5.3%(1/19)was S.agalactiae strains.Between 2009 and 2012,the dominant strains,however,became S.agalactiae,which accounted for 96.6%(56/58),only 3.4%(2/58)was referred as S.iniae strains.The strains were divided into two branches by PFGE genotyping.20 S.iniae strains were in one classification with 4 PFGE genotypes,the similarities of which were 83.9%-100%.17 S.agalactiae strains were put in another branch with 5 PFGE genotypes,the similarities of which were between 47.4% and 100%.Our data confirmed that the prevalent strains of tilapia Streptococcus spp.in Guangxi province have been shifting from S.iniae(before 2008)to S.agalactiae(2009-2012),and the PFGE genetic diversities were demonstrated in the prevalent strains.