Objective To investigate the species composition, functionality, and drug resistance of vaginal microbiota under different Group B Streptococcus (GBS) colonization statuses in late pregnancy, and to provide foundational data for understanding the interaction and impact between GBS colonization and the vaginal microecology.

Methods Vaginal swab samples were collected from pregnant women undergoing prenatal GBS screening in late pregnancy. Samples positive for GBS were identified through conventional clinical microbiological culture. Simultaneously, samples negative for GBS culture from pregnant women with similar baseline characteristics were selected as controls. DNA was extracted from the selected samples, and metagenomic sequencing was performed. Bioinformatics analysis was used to compare the composition and differences in vaginal microbial populations, metabolism, and resistance-related genes between the GBS-positive and GBS-negative groups, aiming to explore the impact of GBS colonization on the vaginal microbiota.

Results Among 150 samples, 13 tested positive for GBS culture. Matched 16 GBS culture-negative samples were selected as controls. Metagenomic sequencing analysis revealed that the diversity of vaginal microbiota in the GBS-positive group was significantly lower than that in the negative group (P<0.05). Microbial differential analysis indicated that the GBS-negative group was predominantly colonized by protective Lactobacillus species such as Lactobacillus crispatus (LDA = 5.274, P<0.01) and Lactobacillus jensenii (LDA= 4.072, P<0.05). In contrast, the GBS-positive group showed significant enrichment of Lactobacillus iners (LDA=5.528, P<0.001), with an increased proportion of opportunistic pathogens. Significant differences were observed between the two groups in microbial functions and metabolic pathways (P<0.05), as well as in categories of antibiotic resistance genes, including macrolides, polypeptides, and Macrolide-Lincosamide-Streptogramin B (MLS) (P<0.05). Specifically, the relative abundance of the macrolide resistance gene ermB was significantly higher in the GBS-positive group compared to the negative group (P<0.05).

Conclusions The vaginal microenvironment in late pregnancy differs significantly based on GBS colonization status. GBS-positive colonization is associated with reduced microbial diversity, decreased abundance of beneficial Lactobacillus species, and increased relative abundance of resistance genes. These findings suggest that GBS colonization during pregnancy may be related to the vaginal microenvironment. Improving the vaginal microenvironment could potentially reduce vaginal GBS colonization, thereby safeguarding maternal and neonatal health.