Abstract
Candida‐associated denture stomatitis presents as erythema of the palatal mucosa and is caused by biofilms containing the fungus Candida albicans that co‐reside with oral bacteria on the denture‐fitting surface. This study aimed to assess the effect of several frequently encountered oral bacteria on the expression of C. albicans virulence factors in in vitro polymicrobial biofilms. Biofilms containing C. albicans and selected bacterial species were grown on denture acrylic, and analysed by microscopy and by qPCR for expression of putative virulence genes. Candida albicans‐only biofilms showed limited hyphal production. Hyphal development was significantly (P < 0·001) increased when biofilms also contained four species of oral bacteria (Streptococcus sanguinis, Streptococcus gordonii, Actinomyces odontolyticus and Actinomyces viscosus), as was the expression of virulence genes (P < 0·05). Importantly, inclusion of Porphyromonas gingivalis in the biofilm consortium resulted in significant (P < 0·05) inhibition of virulence gene expression and production of hyphae. The in vitro expression of C. albicans virulence factors was modulated in polymicrobial biofilms. The complexity of this modulation was highlighted by the reversal of effects following introduction of a single bacterial species into a biofilm community.Significance and Impact of the StudyThe impact of individual bacterial species on Candida albicans virulence highlights both the complexity of predicting infection mediated by polymicrobial communities and the potential for management through pro‐ or prebiotic therapy. The possibility to selectively modulate microbial virulence by addition of, or treatment with pro‐ or prebiotics avoids the use of conventional antimicrobial compounds, thus reducing the contribution to potential drug resistance. Understanding which bacterial species modulate virulence, and the mechanisms by which this occurs, particularly in biofilms, provides excellent foundations for further research questions, and the potential for novel clinical interventions.
Highlights
We have previously shown that co-culturing C. albicans with a range of oral bacteria in biofilms on denture acrylic materials resulted in enhancement of C. albicans virulence (Cavalcanti et al 2015; Morse et al 2018)
Culture of C. albicans biofilms without other microorganisms resulted in limited hyphal development (Table 1), which were at a basal level in the biofilm structure (Figs 1a and 2)
Biofilms containing C. albicans with mixed-species of oral bacteria resulted in over a 12-fold increase in the proportion of hyphae relative to yeast cells (Figs 1b and 2), which was statistically significant (P < 0Á001)
Summary
The fungal genus Candida consists of a number of important species (Haynes 2001; Ganguly and Mitchell 2011; Patil et al 2015), some of which are implicated in localized and systemic human infection (Ganguly and Mitchell 2011; Patil et al 2015) These infections are known as candidoses (Scully et al 1994; Williams and Lewis 2011), and tend to occur in people with one or more predisposing factors, including a weakened immune system, diabetes, human immunodeficiency virus (HIV)/ acquired immune deficiency syndrome (AIDS) or altered microbiota as a result of antibiotic or steroid use (Williams and Lewis 2011; Patil et al 2015). While symptoms of itching, burning or generalized oral discomfort may be mild, their chronic nature necessitates management and treatment
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