Neonatal colonization of group B Streptococcus in China: Prevalence, antimicrobial resistance, serotypes, and molecular characterization.

BACKGROUND: Group B Streptococcus (GBS) remains a leading cause of neonatal mortality and morbidity. This study aimed to determine the prevalence, antimicrobial susceptibility, serotypes, and molecular characterization of GBS colonized in neonates.

METHODS: A cross-sectional study was conducted using a multistage sampling method. Swabs for GBS identification were taken from infants' ear, oral cavity, and umbilicus immediately after birth. All GBS isolates were tested for antimicrobial susceptibility, resistance genes, serotyping, multilocus sequence typing, and virulence genes.

RESULTS: Of the 1,814 neonates, 1.3% tested positive for GBS, with 66.7% tested as multidrug resistant. All GBS isolates were susceptible to penicillin, but rates of resistance to tetracycline and erythromycin were high (70.8%), with the predominant resistance genes being tetM and ermB. The predominant serotype was III, followed by Ia and Ib, and the most common genotypes were sequence type (ST) 19, ST10, and ST485. Notably, we found that ST19 and ST17 isolates were associated with serotype III, resistant to tetracycline, erythromycin, and clindamycin, and carrying ermB, tetM, and rib; ST10 and ST12 isolates were associated with serotype Ib, resistant to erythromycin and clindamycin, and carrying ermB and alphaC; and ST485 isolates were associated with serotype Ia and carrying mefA/E, tetM, and epsilon.

CONCLUSIONS: These findings indicate a high prevalence of multidrug-resistant GBS and specific phenotype-genotype combinations for GBS clones.