S. agalactiae Promote G. vaginalis Biofilm Formation Leading to Recurrence of Bacterial Vaginitis

Abstract Bacterial vaginosis (BV) is a condition with a high short-term cure rate and a high recurrence rate. The formation of Gardnerella vaginalis （GV） biofilm is one of the primary reasons for BV recurrence. This study was the first to explore the impact of Streptococcus agalactiae(group B Streptococcus, GBS), a symbiotic intravaginal bacterium, on G. vaginalis concerning biofilm biomass, biofilm structure, transcriptome, and proteome in a co-culture scenario. The results revealed that the supplementation of GBS to G. vaginalissignificantly increased the biomass in 48-hours dual-species biofilms. As confirmed by qPCR, the differentially expressed gene (DEG) luxS of GBS identified through transcriptome analysis was significantly higher in dual-species biofilm compared to mono-species biofilm. Subsequently, we developed a GBS luxS mutant strain (ΔGBS) and observed significant reductions in ΔGBS biofilms and ΔGBS+GV dual-species biofilms. Upon supplementing with exogenous AI-2 reagents, there was a substantial increase in biofilm biomass noted in GBS, ΔGBS, and GV mono- and dual-biofilms. Furthermore, we found that the expression of two genes related to biofilm formation, murG and GAVG_RS05105, was significantly elevated in GV after receiving AI-2 signals. Collectively, these findings suggest that GBS enhances biofilm formation by luxS/AI-2 in an in vitro co-culture model, potentially offering a new approach for treating RBV.