The Study Of Molecular Typing And Recombination In Group B Streptococcus

Aim:Capsular polysaccharide(CPS)genes and pilus islands genes were important virulence factors for Group B Streptococcus(GBS).This study aims to detect molecular typing in CPS genes and pilus islands genes in GBSs and to explore the relationship with genetic recombination and pathogenic phenotype(invasiveness)of the isolates.Materials & methods:Whole genome sequencing was performed on 21 clinical GBS isolates,and a total of995 GBS genomes that have been published were downloaded from the NCBI public database.The multilocus sequence typing(MLST)and Bayesian analysis of Population Structure(BAPS)analyses were both performed,and the phylogeny construction was built.Based on whole genome sequencing,the Basic Local Alignment Search Tool database was built for molecular typing of CPS and pilus islands genes.Recombination was defined in this study as the inconsistencies between phylogeny and the CPS as well as pilus typing results.Isolates was divided as being invasive or colonizing based on the source information.Results:The seven genes used for MLST in GBS had been not found any recombination yet,and ST17(9.1%)was the most prevalent.All the CPS typing and pilus typing results were generally consistent with MLST and BAPS clustering,and CPS Ⅱ(24.6%)and PI-1 + PI-2a(39.2%)were the most prevalent.However,recombination still existed among CPS genes and pilus islands genes.GBS isolates of CPS Ⅱ and of the PI-1 +PI-2b and PI-2a types were more prone to recombination than the others.Isolates of the CPS types Ib,Ia and PI-1 + PI-2a type were the most reluctant to recombine.Isolates of CPS Ib and of the PI-1 + PI-2a type were more likely to appear as colonizing strains,whereas PI-2b type was more likely to appear in invasive strains.For CPS V,recombination occurred more commonly in colonizing isolates,while for CPS Ⅲ,the opposite occurred.Conclusion:This study found that CPS Ⅱ and PI-1 + PI-2a were the most prevalent;CPS Ⅱ and the PI-1 + PI-2b and PI-2a types were more prone to recombination than the others;PI-2b type was more likely to appear in invasive strains;for CPS V,recombination occurred more commonly in colonizing isolates.This is helpful for infection control and the development of new vaccines for the prevention of GBS occurrence.