Abstract

Introduction Streptococcus agalactiae (Group B Streptococcus, GBS) is a Gram-positive opportunistic pathogen and a leading cause of invasive infections in neonates and pregnant women worldwide. Pathogenicity and transmission dynamics are shaped by capsular serotypes, clonal backgrounds, and virulence and resistance determinants, which vary over time and by region. Data from South China remain limited. This study characterized the serotype distribution, sequence types (STs), clonal complexes (CCs), antimicrobial resistance genes, and virulence factors of clinical GBS isolates from Guangzhou.Methods GBS-positive clinical isolates collected at Guangdong Provincial People’s Hospital (Guangzhou, China) from 2016 to 2022 were subjected to genomic epidemiology analyses. A total of 72 non-duplicate isolates were included. Multilocus sequence typing (MLST) and whole-genome sequencing (WGS) were used to determine capsular serotypes, sequence types (STs) and clonal complexes (CCs), and to identify antimicrobial resistance genes and virulence determinants, including pilus islands.Results Among 72 isolates, serotype III predominated (36.1%), followed by serotype V (25.0%). Isolates were assigned to 22 STs within 7 CCs, with ST19 being most common (15.3%). Resistance gene profiling showed tetM in 61.1% of isolates and ermB in 37.5%. Virulence factor analysis indicated universal presence of lmb, bca, and cpsJ; 97.2% carried the hemolysin gene hlyB. Pilus island genes PI-1 and PI-2a were detected in 73.6% of isolates.Discussion GBS circulating in Guangzhou shows a serotype distribution dominated by III and V and a diverse clonal structure with ST19 prominence. The high carriage of tetM and ermB suggests sustained selective pressure for tetracycline and macrolide resistance, while the near-ubiquitous virulence repertoire—including lmb, bca, cpsJ, and hlyB—and frequent PI-1/PI-2a may support colonization and invasiveness. These findings highlight the need for ongoing, region-specifi