Annabel Sabine Hinderfeld, Niha Phukan, Augusto Simoes-Barbosa
The human vaginal tract harbours a large number of microbes believed to play an important role in influencing the outcome of vaginal infections. In recent years, studies have differentiated the natural vaginal microbiota into so called community state types (CST) I / II / III / V, which are dominated by different Lactobacillus species, whereas community state type IV is defined by a species-diversified composition of the microbiota and the absence of lactobacilli. The human protozoan Trichomonas vaginalis, the causative agent of the most prevalent non-viral sexually transmitted disease is commonly accompanied by CST-IV. Interestingly, CST-IV includes species associated with another common vaginal infection, bacterial vaginosis (BV). Both infections are associated with the transmission of human immunodeficiency virus (HIV) and gynaecological complications, which likely are a result from the disruption of the cervicovaginal epithelial barrier. However, key aspects of the complex interaction between the parasite and anaerobic bacteria of CST-IV associated with BV and the protective mechanisms of lactobacilli remain elusive. We showed that T. vaginalis and BV - associated bacteria (BVB) cooperatively interact to enhance paracellular permeability of the cervicovaginal epithelium by dysregulating Tight Junctions. Our group also reported that BVB increase the adhesion properties of a previously low adherent strain of T. vaginalis (G3) and that this effect is time-and contact-dependent. In addition, we reported that the inhibitory effects of Lactobacillus gasseri (CST-II) against the adhesion of T. vaginalis to host cells is contact-dependent as well and that bacterial surface proteins are largely responsible for this inhibitory phenotype. We found that the aggregation-promoting factor APF-2 from this bacterium significantly contributes to the inhibition of the adhesion of T. vaginalis to human vaginal ectocervical cells. Our studies highlight the importance of understanding the interaction between pathogens and the microbiota and their implications on human health and disease as well as to help develop novel and specific therapeutic strategies.