Impact of the Antifungal Fluconazole on Streptococcal Growth and Oral Microbial Biofilms
Objectives: Antifungals have the potential to disturb the balance of microbial communities in the gut. While this effect is mainly attributed to the direct effect on fungal populations in the gut and possible host cytotoxic effects, less is known about its potential anti-bacterial effect or the impact on the microbiota in other body sites. The objective of this study was to evaluate the effect of fluconazole on streptococcal growth and oral biofilms.
Methods: The Streptococcus strains, S. mitis MI048 and S. mutans SM120, had a Pldh-luc reporter for growth assessment in planktonic cultures. For the oral biofilms, we used an ex vivo model enabling the growth of a highly complex microbial community. Fluconazole was assessed at different concentrations: salivary (2,6 μg/mL), ½ peak plasma (2,2 μg/mL), peak plasma (4,4 μg/mL), 2x peak plasma (8,8 μg/mL), and at a mouth rinse concentration (2 mg/mL).
Results: The highest fluconazole concentrations resulted in increased viable counts of streptococci and total microorganisms in the oral microbiome biofilm model, despite a tendency for reduced biomass and similar pH values by the end of the experiment. In the planktonic assay, the highest fluconazole concentrations reduced and delayed the growth of S. mitis, while no significant effect was observed for S. mutans growing under similar conditions, or in S. mitis grown as biofilms.
Conclusions: Although fluconazole is used as an antifungal agent, our results suggest that it may have an antibacterial effect against oral streptococci and impact the development of oral microbial biofilms. The findings are of relevance, given the importance of microbial homeostasis for human health, together with current challenges related to the increase in antibiotic resistance and the need for new strategies to fight infections.