Molecular characteristics of Group B Streptococcus isolates from Daqing, Heilongjiang Province, China

Streptococcus agalactiae (Group B Streptococcus, GBS) is an important opportunistic pathogen associated with invasive infections in neonates, pregnant women, and immunocompromised adults, while increasing antimicrobial resistance poses challenges for clinical management. This study investigated the distribution, antimicrobial susceptibility, and molecular characteristics of GBS isolates collected from a tertiary hospital in Daqing, northeastern China. A total of 1,040 non-duplicate GBS isolates collected from outpatients and inpatients between 2020 and 2025 were analysed for specimen distribution and antimicrobial susceptibility. Molecular characterization was performed on 118 archived isolates using multiplex PCR for capsular serotypes, antimicrobial resistance genes, and virulence genes, together with the D-test for macrolide resistance phenotypes. The GBS carriage rate among women in late pregnancy was 6.0% (397/6,669). All isolates were susceptible to penicillin, ampicillin, vancomycin, linezolid, and tigecycline, while the resistance rates to erythromycin, clindamycin and levofloxacin were 93.2, 78, and 66.1%, respectively. Among the 118 characterised isolates, serotype Ib predominated (74.6%), followed by serotypes III (15.3%) and Ia (10.2%). The ermB (83.9%) and ermC (53.4%) genes were the predominant macrolide resistance determinants, and the constitutive MLSB (cMLSB) phenotype was the most common macrolide resistance phenotype (73.7%). These findings provide regional data on the antimicrobial susceptibility and molecular characteristics of GBS in northeastern China.