Genetic diversity and new genotyping scheme for fish pathogenic Streptococcus agalactiae

Abstract

This study aimed to assess the genetic diversity of fish isolates ofStreptococcusagalactiaeby capsular serotyping, MLST and the pattern of selected virulencegenes. Forty-six isolates from Nile tilapia and Amazon catfish were screened byPCR for the twelve virulence genes.The molecular capsular type and sequencetype (ST) were determined. Two capsular types (Ia and Ib) and four STs (103,260, 552 and 553) were identified. The ST-552 and ST-553 represent newallelic combinations. Variable results were found for the genesgbs2018-6,lmb,hylBandcylE.The combined evaluation of serotype, sequence type and patternof the presence or absence ofcylEandhylBallowed the classification of isolatesinto nine genetic profiles (I–IX). The proposed scheme showed higherdiscriminatory power and was able to detect evolutionary events missed byMLST analysis. This study provides new information about the geneticdiversity of fish pathogenicStrep. agalactiae,and the proposed scheme wasshown to be an improved approach to genotyping these strains.