Gut microbiota and short-chain fatty acids in pregnant women with group B Streptococcus colonization and their impact on neonatal outcomes.

BACKGROUND: Group B Streptococcus (GBS) frequently colonizes the gastrointestinal and lower reproductive tracts in pregnant women. However, research has predominantly addressed its influence on the vaginal microbiota, leaving its effects on the gut ecosystem and the consequent implications for neonatal outcomes largely unexplored. METHODS: In this prospective study, 87 pregnant women were enrolled at the Women and Children's Hospital of Xiamen University from March 2022 to October 2023 and divided into GBS-positive and GBS-negative cohorts according to their colonization status. Fecal samples were collected to complete 16S rRNA gene sequencing and fecal Short-chain fatty acids (SCFAs) content determination. The pregnancy outcomes and clinical prognosis information of the newborns were followed up. Intestinal microbiota composition and SCFAs levels were compared between GBS-positive and GBS-negative pregnant women, and their respective correlations with pregnancy and neonatal outcomes were evaluated. RESULTS: Significant differences in the genera Ruminococcus, Klebsiella, and Intestinibacter were observed between GBS-positive and GBS-negative group. SCFAs-targeted metabolomic analysis revealed that fecal butyrate concentration were significantly lower in GBS-positive group than in GBS-negative group. Association analysis revealed a significant positive correlation between intestinal butyrate concentration and the abundance of Ruminococcus (ρ = 0.216, P = 0.045). Spearman's correlation analysis showed that Ruminococcus abundance and butyrate concentration were positively correlated with birth weight percentile-Fenton of newborn (ρ = 0.390, P < 0.001; ρ = 0.403, P < 0.001) and negatively correlated with umbilical cord blood IL-6 level (ρ = -0.229, P = 0.033; ρ = -0.445, P < 0.001). After adjusting for confounding factors including GBS colonization, regression analysis showed that increased butyrate concentration was an independent protective factor against elevated IL-6 (aβ: -27.823, 95%CI: -50.041~-5.606), whereas increased incidence of chorioamnionitis was an independent risk factor for elevated IL-6 (aβ: 30.155, 95%CI: 2.556~57.754). CONCLUSIONS: GBS colonization in late pregnancy is associated with disruptions in the gut microbiota and its metabolic profiles, particularly with lower Ruminococcus abundance and diminished butyrate metabolism. Butyrate may lower neonatal inflammation through anti-inflammatory mechanisms. Therefore, targeting Ruminococcus or the butyrate metabolic pathway should be viewed as a hypothesis-generating strategy to improve perinatal outcomes in GBS-colonized pregnant women.