Contribution of Oral Bacteria to Candida Virulence and Denture Stomatitis

Objectives: The oral infection, denture-associated stomatitis (DS), affects up to 60% of denture-wearers, presenting as areas of palatal inflammation. It is associated with microbial biofilms containing Candida albicans on denture-fitting surfaces. The contribution of oral bacteria within these biofilms to infection is unclear, therefore research demonstrating the in-vitro impact of bacteria upon infection prognosis is necessary to improve treatment regimes. This in vitro study evaluated the impact of bacteria on Candida virulence, and evaluated bacterial microbiomes at specific oral sites in DS and non-DS patients to determine associations with infection.
Methods: In vitro biofilm studies assessed expression of C. albicans virulence factors (morphological transformation, adhesins, hydrolytic enzymes), and their impact on pathogenesis in an infection model. Microbiological specimens were clinically obtained from the tongue, palate and denture-fitting surface of 19 denture-wearing patients (DS n=8, non-DS n=11). Bacterial DNA was extracted and differences in the bacterial microbiomes determined by next generation sequencing using 16S rRNA gene targets.
Results: Certain oral bacterial species significantly (P<0.05) modulated C. albicans virulence factor expression. In biofilms where virulence was enhanced, substantially enhanced tissue damage in model systems was observed. Metataxonomic analyses revealed a significant (P=0.007) increase in the number of bacterial species (diversity) in samples of the tongue of non-DS patients, but no significant differences between DS and non-DS patients when considering the denture-fitting and palate surfaces. Differences in the relative abundance of bacterial species common to both DS and non-DS patients, at other sample sites were also evident.
Conclusions: The in vitro modulating capacity of bacteria toward Candida virulence, and the observed species-level differences in bacteria between DS and non-DS patients highlight the need for consideration of the bacterial composition of oral biofilms in understanding the pathogenesis of DS and its management.