Use of probiotic bacteria to selectively modulate Candida albicans virulence in biofilms

Candida albicans is an opportunistic fungal pathogen present in the oral cavities of up to two-thirds of people. Despite typically existing as a commensal microorganism, it has pathogenic potential, particularly in older, immunocompromised individuals. A common Candida-associated infection is denture-associated stomatitis (DS), which presents clinically as areas of erythema on the palatal mucosa, and discomfort for the denture-wearer. In vitro, previous work has shown that the expression of C. albicans virulence factors varies according to its interactions with other oral microorganisms.

Mature single- and mixed-species biofilms (with Candida and several strains of common oral bacteria) were grown on poly(methyl methacrylate) (PMMA) coupons, representing dentures. Additionally, to some coupons, individual probiotic strains were added. Total RNA was extracted, reverse transcribed and putative virulence gene expression was determined by RT-qPCR relative to ACT1, a housekeeping gene. Biofilm-infection assays of FADU and TR146 epithelial cell lines were also performed by pre-culturing cells, then adding single- or mixed-species inocula overnight. Quantification of cell damage determined by lactate dehydrogenase assay.

Biofilm co-culture with the addition of certain probiotic strains downregulated C. albicans virulence genes in both short-term and long-term mixed-species biofilms. With an increasing aged population that is heavily reliant on the use of antibiotics that can negatively affect the microbiota of patients, there is a requirement to look at the benefits of prophylactics, from both an economic and patient well-being viewpoint. The results show the realistic possibility of using probiotics to prevent or restrict development of Candida-associated oral diseases.