Genomic Characterization of Clinical Group B Streptococcus Isolates from Zhejiang, China: Serotypes, Clonal Complexes, and Predicted Antimicrobial Resistance and Virulence Gene Profiles

This study aimed to characterize the population structure, predicted antimicrobial resistance gene profiles, and virulence gene repertoire of Group B Streptococcus (GBS) in Zhejiang Province, China, using whole-genome sequencing (WGS). Forty GBS isolates from clinical specimens underwent WGS, multilocus sequence typing (MLST), cgMLST-based phylogenetic analysis, and systematic in silico annotation of predicted antimicrobial resistance and virulence genes. Seven capsular serotypes were identified, with serotype V being predominant. Fifteen sequence types (STs) were detected, including two novel STs (ST2662 and ST2663). Thirteen STs were grouped into eight clonal complexes (CCs), while two STs remained unassigned to any CC. CC19 (11/40, 27.5%) and CC327 (10/40, 25.0%) were the predominant CCs, with CC327 comprising the distinctive ST529-CC327-V clone. Eighteen predicted antimicrobial resistance genes were identified, including genes predicted to confer resistance to macrolide (ermB 60.0%, mefA 37.5%), tetracycline (tetM 47.5%, tetO 42.5%), aminoglycoside (aph(3′)-IIIa 25.0%), and lincosamide (lsaE 30.0%, lnuB 30.0%). All isolates carried multiple predicted virulence genes, with universal carriage of adhesion genes fbsA and fbsB, and the invasion genes cylE, hylB, and cfb. These findings reveal a genetically diverse GBS population with distinctive clonal architecture and high carriage of predicted antimicrobial resistance genes in Zhejiang Province, underscoring the need for continued genomic surveillance to inform region-specific antibiotic stewardship and vaccine development.