Candida albicans and NCAC species: acidogenic and fluoride-resistant oral inhabitants.

Objective: Although Candida species are thought to contribute to dental caries, their acid production under anaerobic conditions and susceptibility to fluoride have not been thoroughly studied. We therefore investigated the growth, acid production, and effect of fluoride on Candida species.

Methods: Aerobic growth, acid production from glucose and its end-products under aerobic and anaerobic conditions, and enolase activity were measured in C. albicans and non-Candida-albicans-Candida (NCAC) species (C. tropicalis, C. parapsilosis, C. maltosa, and C. glabrata), and the effect of fluoride on these abilities was evaluated.

Results: All Candida species produced acids under aerobic and anaerobic conditions, and acetate and TCA cycle metabolites were detected. However, these organic acids only accounted for 1.9-57.6% of the acids produced. Up to 80 mM fluoride hardly inhibited growth and did not inhibit acid production except for C. glabrata, despite the low 50% inhibitory fluoride concentration of 0.19-0.34 mM for enolase.

Conclusion: Candida species produced acids under aerobic and anaerobic conditions, indicating their significant cariogenicity. Their growth and acid production were highly fluoride-resistant, whereas their enolase was fluoride-sensitive, suggesting mechanisms for maintaining low intracellular fluoride. The mechanisms underlying the fluoride resistance remain underexplored. Approaches other than fluoride may be needed to control Candida-associated caries.