Candida albicans as an Essential “Keystone” Component within Polymicrobial Oral Biofilm Models?

Abstract

Background: Existing standardized biofilm assays focus on simple mono-species or bacterial-only models. Incorporating Candida albicans into complex biofilm models can offer a more appropriate and relevant polymicrobial biofilm for the development of oral health products. Aims: This study aimed to assess the importance of interkingdom interactions in polymicrobial oral biofilm systems with or without C. albicans, and test how these models respond to oral therapeutic challenges in vitro. Materials and Methods: Polymicrobial biofilms (two models containing 5 and 10 bacterial species, respectively) were created in parallel in the presence and absence of C. albicans and challenged using clinically relevant antimicrobials. The metabolic profiles and biomasses of these complex biofilms were estimated using resazurin dye and crystal violet stain, respectively. Quantitative PCR was utilized to assess compositional changes in microbial load. Additional assays, for measurements of pH and lactate, were included to monitor fluctuations in virulence “biomarkers.” Results: An increased level of metabolic activity and biomass in the presence of C. albicans was observed. Bacterial load was increased by more than a factor of 10 in the presence of C. albicans. Assays showed inclusion of C. albicans impacted the biofilm virulence profiles. C. albicans did not affect the biofilms’ responses to the short-term incubations with different treatments. Conclusions: The interkingdom biofilms described herein are structurally robust and exhibit all the hallmarks of a reproducible model. To our knowledge, these data are the first to test the hypothesis that yeasts may act as potential “keystone” components of oral biofilms.

Chitosan Enhances the Anti-Biofilm Activity of Biodentine against an Interkingdom Biofilm Model

“…These results indicate that fungi may confer protection to bacteria from active agents when grown in mixed microbial culture. This is in line with that described by Young, Alshanta [55], where protection to antimicrobial challenge is conferred upon bacterial species in the presence of C. albicans. It has also been shown that C. albicans ECM protected S. aureus against vancomycin treatment, possibly by limiting or delaying drug diffusion to S. aureus [56].…”

An In Vitro Evaluation of Denture Cleansing Regimens against a Polymicrobial Denture Biofilm Model

“…Candida is essential for supporting the growth of bacteria. C. albicans offers a structural scaffold for other organisms to adhere [ 10 , 23 ]. Therefore, a polymicrobial biofilm model containing both bacteria and fungi was used.…”

The Role of Candida albicans Virulence Factors in the Formation of Multispecies Biofilms With Bacterial Periodontal Pathogens

“…Both biofilms and biofilm supernatants significantly induced the increase of TNF-a and IL-8 at the gene and protein levels (Bhardwaj et al, 2020). In a recent study by Young et al (2020), two biofilm models were used to investigate the role of C. albicans in the multispecies community. The first model of hard tissue related to caries initially involved a 24-h co-incubation of two pioneering species, C. albicans laboratory strain 3153A and S. mutans (10 7 CFU/ml of bacteria and fungi in an equal volume), followed by the addition of a mixture of four species-F. nucleatum, A. naeslundii, Veillonella dispar, and Lactobacillus casei (10 7 CFU/ml for each bacterium), which were co-incubated for the next 4 days to form a biofilm structure.…”

“…Recently, the studies conducted by Young et al (2020) concerning the role of C. albicans as a keystone commensal in polymicrobial oral biofilms associated with periodontitis/denture stomatitis showed that the presence of fungi in such biofilm did not affect their susceptibility to short-term used biofilm eradication agents. Such biofilms were formed in the presence or absence of C. albicans by S. oralis, S. mitis, S. intermedius, F. nucleatum, F. nucleatum ssp vincentii, Actinomyces naeslundii, Veillonella dispar, P. gingivalis, P. intermedia, and A. actinomycetemcomitans and then analyzed for biofilm thickness and metabolic activity, as well as for bacterial and fungal load following 10-min treatment with chlorhexidine gluconate, EDTA, potassium iodide, or antifungal drug miconazole (Young et al, 2020). These studies showed that under the conditions applied, the presence of C. albicans in multispecies biofilm did not provide significant protection for the microbiota against the range of treatment agents used, compared with bacterial biofilms formed without fungi.…”