Group B Streptococcus and the Vaginal Microbiota

Abstract

Background: Streptococcus agalactiae (group B Streptococcus [GBS]) is an important neonatal pathogen and emerging cause of disease in adults. The major risk factor for neonatal disease is maternal vaginal colonization. However, little is known about the relationship between GBS and vaginal microbiota.

Methods: Vaginal lavage samples from nonpregnant women were tested for GBS, and amplicon-based sequencing targeting the 16S ribosomal RNA V3-V4 region was performed.

Results: Four hundred twenty-eight of 432 samples met the high-quality read threshold. There was no relationship between GBS carriage and demographic characteristics, α-diversity, or overall vaginal microbiota community state type (CST). Within the non-Lactobacillus-dominant CST IV, GBS positive status was significantly more prevalent in CST IV-A than CST IV-B. Significant clustering by GBS status was noted on principal coordinates analysis, and 18 individual taxa were found to be significantly associated with GBS carriage by linear discriminant analysis. After adjusting for race/ethnicity, 4 taxa were positively associated with GBS, and 6 were negatively associated.

Conclusions: Vaginal microbiota CST and α-diversity are not related to GBS status. However, specific microbial taxa are associated with colonization of this important human pathogen, highlighting a potential role for the microbiota in promotion or inhibition of GBS colonization.

Keywords: group B Streptococcus; neonatal pathogens; vaginal microbiome.

Figure 1.

Proportion of samples positive for group B Streptococcus (GBS) by community state type (CST). A, There was no evidence of difference of proportion GBS colonized when comparing CSTs (P = .96, Fisher exact test). B, Subgroup analysis within CST IV demonstrated significantly higher prevalence of GBS colonization in CST IV-A than in CST IV-B (P = .001, Fisher exact test).

Figure 2.

Heatmap showing top 25 taxa by community state type (CST) and group B Streptococcus (GBS) status. The samples are organized first by CST (top key), then by GBS status (bottom key).

Figure 3.

Population statistics by group B Streptococcus (GBS) status. A, There was no evidence of difference in α-diversity between GBS-positive and GBS-negative samples based on the chao1 statistic (P = .81) A, Principal coordinates analysis (PCoA) showing the 2 principal coordinates that explained the most variance. B, There was statistically significant clustering of GBS-positive and -negative samples (Adonis P < .001, R² = 0.009).

Figure 4.

Association of specific taxa with group B Streptococcus (GBS) status. linear discriminant analysis effect size output with scores ≥2.5 or ≤ –2.5.

Figure 5.

Correlation between candidate taxa. There were statistically significant positive pairwise correlations between all candidate taxa associated with group B Streptococcus (GBS)–negative status and between the genus Veillonella and Prevotella bivia and the genus Veillonella and the genus Streptococcus (associated with GBS-positive status). Blank boxes indicate no significant pairwise correlation.