Candida albican-bacterial polymicrobial biofilms in recurrent vulvovaginal candidiasis contributes to the drug resistance of the disease: an assessment based on in vivo and in vitro assays

Ten percentage of vulvovaginal candidiasis (VVC) patients experience development of VVC into recurrent VVC (RVVC), which is caused by incomplete eradication of Candida species that form biofilms alone or with bacteria. The purpose of our study was to investigate the effect of types of biofilms on the virulence and antifungal agent resistance of C. albican species. The biofilm formation rate and antifungal agent susceptibility of C. albican strains isolated from VVC or RVVC patients were assessed. In vitro polymicrobial biofilms were induced to assess the association between C. albican strains and bacteria species in RVVC. The data of in vitro experiments was validated with rat models. Among the 186 C. albican strains collected, those isolated from RVVC patients showed higher biofilm formation rates and stronger antifungal agent resistance. Once concatenatedly cultured with bacteria, the polymicrobial biofilms exhibited stronger growth rates than either mono C. albican biofilm. And the higher growth rates of polymicrobial biofilms were associated with stronger resistance to all antifungal agents. With rat models, it was found that colony numbers in vaginal samples isolated from rats injected with mixed microbial suspension were significantly higher than those with C. albican suspension. The histological examination of vaginal samples showed that rats with polymicrobial biofilm were subjected to heavier RVVC symptoms. Findings outlined in our study revealed the high biofilm formation rate and strong antifungal agent resistance of C. albican strains isolated from RVVC and formation of polymicrobial biofilm would strengthen the impairments of C. albican on vagina.