Antimicrobial resistance and molecular characterization of Streptococcus agalactiae from pregnant women in southern China

Introduction: This study aimed to characterize antimicrobial resistance (AMR), molecular determinants of AMR and virulence, as well as clonal relationship of Streptococcus agalactiae isolates from women at 35-37 weeks of gestation in the Chaoshan metropolitan area of southern China. Methodology: Bacterial strains isolated from vaginal swabs were identified and antimicrobial susceptibility tests were performed by using a Vitek 2 Compact system (BioMerieux, France). Resistance and virulence genes were detected by polymerase chain reaction (PCR) and the clonal relationship was analysed by multiple locus variable number tandem repeat analysis (MLVA). Statistical analysis was carried out by using SPSS software, version 19.0. Results: All GBS were susceptible to benzylpenicillin, ampicillin, quinupristin/dalfopristin, tigecycline, linezolid and vancomycin, but a considerable proportion was resistant to clindamycin (29.67%), erythromycin (46.15%), azithromycin (63.74%), tetracycline (84.62%) and quinolones (25.27%). The carrier rates of ermB (69.04%) and mefA/E (64.28%) were detected in these GBS strains resistant to erythromycin. In terms of MLVA detection, 91 GBS strains were categorized into 43 genotypes and 6 clusters. All GBS harboured hylB and cylE genes, most of which carried a combination of PI-1 and PI-2a genes as a common virulence gene profile. Conclusions: The high level of resistance conferred by some corresponding resistance genes to macrolides, lincosamides and quinolones of GBS isolates from pregnant women in southern China, has reinforced the necessity for monitoring GBS strain resistance to the above agents. Comparative genetic studies of GBS isolates, especially efforts to understand the relationship between piles islands and genotype, were essential for conducting infection control and epidemiological comparisons between countries.