Background: The complex vaginal flora is not only harbouring lactobacilli but also viridans group streptococci (VGS). Some lactobacilli have an inhibitory effect on group B streptococci (GBS) and other pathogenic bacteria in vitro. If other commensal vaginal bacteria also have inhibiting effect on GBS is less well known.
Material and methods: Clinical isolates of vaginal lactobacilli and VGS from healthy women were collected. In vitro methods like agar over-lay, PBS supernatant test and co-culturing in broth was tested under different pH conditions. A pilot test on two women with vaginal colonization with GBS using a vaginal crème with Lactobacillus plantarum and Streptococcus oralis during a three week period was also performed.
Results: Several isolates of Lactobacillus sp. could inhibit growth and also kill GBS in the in vitro test. However, when pH was higher than pH 6,0 this inhibiting effect was less effective. Some isolated VGS could also inhibit growth of GBS and the results were not depending on pH. There was also a synergistic killing effect of Lactobacillus plantarum strains together with several VGS strains (S.sanguinis, S.oralis, S.salivarius). The two GBS colonized women had negative GBS cultures in vaginal samples after using a cream with Lactobacillus plantarum and Streptococcus oralis.
Conclusion: Commensals as lactobacilli are important for a healthy balance in the vaginal microbiota. Should also VGS be considered in this respect? Some of these strains can inhibit growth of GBS in vitro and together with Lactobacillus plantarum have synergistic killing effect.