In vitro impact of fluconazole on oral microbial communities, bacterial growth and biofilm formation

Anti-fungal agents are widely used to specifically eliminate infections by fungal pathogens. However, the specificity of anti-fungal agents has been challenged by a few studies demonstrating anti-bacterial inhibitory effects against Mycobateria and Streptomyces species. Here we evaluated for the first time the potential effect of fluconazole, the most clinically used antifungal agent, on a human oral microbiota biofilm model. The results showed that biofilm viability on blood and mitis-salivarius agar media was progressively increased in the presence of fluconazole at clinically relevant concentrations, despite of a reduction in biomass. Target PCR revealed higher proportions of Veillonella atypica, Veillonella dispar and Lactobacillus spp. in the fluconazole treated samples compared to the control, while Fusobacterium nucleatum was reduced and Streptococcus spp was not significantly affected. Further, we tested the potential impact of fluconazole using single-species models. Our results using Streptococcus mutans and Streptococcus mitis luciferase reporters showed that S. mutans planktonic growth was not significantly affected by fluconazole, while for S, mitis planktonic growth, but not biofilm viability, was inhibited at the highest concentration. Fluconazole effects on S. mitis biofilm biomass were concentration and time-dependent. Exposure for 48h to the highest concentration of fluconazole was associated with S. mitis biofilms with the most increased biomass. Potential growth inhibitory effects were further tested using four non-streptococcal species. Among these, planktonic growth of both Escherichia coli and Granulicatella adiacens were inhibited by fluconazole. Conclusions: The data indicate bacterial responses to fluconazole that extend to a broader range of bacterial species than previously anticipated from the literature, with the potential to disturb microbial biofilm communities. Future studies are warranted to further identify the breath of species for which growth may be impacted by anti-fungal agents, and possible mechanisms involved.