The influence of lactobacilli on the adhesion of the parasite Trichomonas vaginalis to host vaginal epithelial cells

Abstract

Trichomonas vaginalis is an obligate human pathogen that is the causative agent of the sexually transmitted disease, trichomoniasis. This infection is one of the most frequent sexually transmitted diseases in the world, with approximately 180 - 200 million cases reported annually. As an extracellular organism T. vaginalis must adhere to host epithelial cells to successfully infect and survive, thus, adhesion is a critical part of pathogenesis. Inflammation of different parts of the female and male urogenital tract such as urethra, vaginal, cervix, epididymis and prostate suggests that the parasite is capable of inhabiting numerous host environments. These niches are constantly changing due to external factors as well as host biological processes. These changes include hormonal shifts leading to epithelial shedding in females, excretion causing changes in salinity, pH and toxicity, and flux in the microorganisms naturally inhibiting or infecting the environment. Lactobacillus species are the most prevalent organisms in normal human vaginal flora and have been reported to protect the vaginal environment against various urogenital pathogens and sexually transmitted infections. Although, T. vaginalis adhesion has been investigated previously by numerous studies, all of these studies have been monoculture models of infection, ignoring the influence of lactobacilli. Here we originally considered the influence of different Lactobacillus isolates, on the adhesion of parasite to vaginal epithelial cells. The quantification of parasite adhesion was done using a newly developed flow cytometry methodology. We were able to measure the influence of forty-one Lactobacillus isolates on the adhesion of the T. vaginalis. In addition, this rapid methodology enabled us to take a multi-parametric approach to the analysis of this microbial interaction - looking at the adhesion properties of multiple strains of T. vaginalis, and varying several other parameters of incubation. These included: cell ratio, pH, incubation modes (order in which cells were brought to contact), and whether or not the interaction between parasite and bacterium was contact-dependent. In addition, we examined the possible participation of T. vaginalis surface lipophosphoglycans (LPGs) in the mechanisms of influence of lactobacilli on parasite adhesion properties. All together, these approaches gave us important insights into this interaction. Our observations have indicated that the majority of lactobacilli influence the adhesion of T. vaginalis, therefore, we are now confident that the adhesion of this pathogen to host cells (and possibly many other virulence aspects) cannot ignore the participation of lactobacilli and that trichomoniasis must be studied in the context of its natural microbiota. Interestingly, the influence of lactobacilli on T. vaginalis adhesion properties depends enormously on the genotype/phenotype of both bacterium and parasite. Our results revealed that parasite adhesion mediated by lactobacilli is influenced by incubation parameters, including; pH, cell dilutions, bacterium:parasite cell ratio, and simultaneous and non-simultaneous incubation of parasite and bacteria. In addition, it was observed that the influence of lactobacilli on T .vaginalis adhesion requires contact between the two microorganisms and that the surface T. vaginalis LPG molecules are not involved in the interaction between these microorganisms. These findings are very significant and will catch the attention of the scientific community.