Biofilm in Genital Ecosystem: A Potential Risk Factor for <i>Chlamydia trachomatis</i> Infection

Abstract

In healthy women, the cervicovaginal microbiota is mostly populated by <i>Lactobacillus</i> spp., the main host defense factor of the female genital tract. In addition to Lactobacilli, other microorganisms populate the cervicovaginal microbiota, like <i>Candida</i> spp. and <i>Gardnerella vaginalis</i>. The overgrowth of <i>Candida</i> spp. or <i>G. vaginalis</i>, known as biofilm-producing microorganisms in the genital ecosystem, may lead to microbial dysbiosis that increases the risk of acquiring sexually transmitted infections, like <i>Chlamydia trachomatis</i>. <i>C. trachomatis</i>, the leading cause of bacterial sexually transmitted diseases, is still considered an important public health problem worldwide because of the impact of asymptomatic infections on long-term reproductive sequelae, including pelvic inflammatory disease and infertility. The aim of our study was to investigate the interaction between <i>C. trachomatis</i> and the biofilm produced by <i>Candida albicans</i> or <i>Gardnerella vaginalis</i>, evaluating whether the biofilm can harbor <i>C. trachomatis</i> and influence its survival as well as its infectious properties. In order to do so, we developed an <i>in vitro</i> coculture transwell-based biofilm model. Our findings proved, for the first time, that <i>C. trachomatis</i>, an intracellular obligate pathogen, survived, for up to 72 hours after exposure, inside the biofilm produced by <i>C. albicans</i> or <i>G. vaginalis</i>, retaining its infectious properties, as evidenced by the typical chlamydial inclusions observed in the cell monolayer (chlamydial inclusion-forming units at 72 h: 9255 ± 1139 and 9873 ± 1015, respectively). In conclusion, our results suggest that the biofilm related to <i>Candida</i> or <i>Gardnerella</i> genital infections may act as a reservoir of <i>C. trachomatis</i> and, thus, contribute to the transmission of the infection in the population as well as to its dissemination into the upper genital tract, increasing the risk of developing severe reproductive sequelae.