Cell-Free Supernatant of Vaginal Viridans Streptococcus Induces Membrane Permeabilization and Transcriptional Regulation in Methicillin-Resistant Staphylococcus aureus

The genus Streptococcus is a heterogenous group of commensal and pathogenic bacteria that are normal inhabitants of the human body, including the female genital tract (FGT). In the FGT microbiome, streptococci represent two major groups: the pathogenic group B Streptococci (GBS) and the commensal viridans group streptococci (VGS). Though members of the VGS are frequently detected from the FGT, their role in the FGT microbiome remains underexplored. Here, we report the characterization of Streptococcus sp. K0074, isolated from the vaginal swab of an endometrial cancer patient admitted to the hospital, with no evidence of bacterial vaginosis. Phylogenetic analysis revealed that the strain is a member of the commensal VGS and possibly represents a novel species in the mitis subgroup. The strain demonstrated the production of low molecular weight bacteriocin-like substance with narrow-spectrum antagonistic activity, affecting the growth, biofilm formation, and colonization of aerobic vaginitis (AV)–causing bacterium methicillin-resistant Staphylococcus aureus (MRSA). The putative bacteriocin exhibited cell membrane–permeabilizing activity and exerted negative regulatory effect on the accessory gene regulator and SaeRS two-component systems of MRSA. Collectively, our results suggest that the isolate may modulate the FGT microbiome by inhibiting or displacing specific pathogen. Furthermore, the results presented here highlight new perspectives regarding the existence of VGS in the FGT microbiome and in particular pinpoint the potential clinical significance of the isolated VGS strain Streptococcus sp. K0074 for the treatment of AV caused by MRSA.