Modeling Dual Species Candida Albicans / Streptococcus Gordonii Oral Biofilms and Their Associated Resistance to Antimicrobial Treatment

Candida albicans is a commensal opportunistic fungal pathogen that resides in mucosal surfaces of the human host, including the oral cavity. As a commensal, C. albicans has been known to interact with the microbiota already found in oral niches and such interactions could potentially affect its colonization and pathogenicity. Streptococcus gordonii, a bacterial organism described as an early colonizer of oral microbiota, has been noted to intimately interact with C. albicans by directly binding to hyphal adhesins. Moreover, S. gordonii has been described to induce filamentation in C. albicans, a key fungal virulence factor. In this work, we describe the development of two in vitro models that permit the study of such fungal-bacterial interactions during the formation of dual-species biofilms. The first one is an adaptation of a 96-well microtiter plate model previously developed for the formation of C. albicans biofilms; whereas the second one involves the growth of mixed biofilms on titanium alloy, the most commonly used biomaterial in dental implants. These models were developed with the use of BMM (Basal Medium Mucin) synthetic saliva in order to simulate physiological conditions found within the oral cavity. Using these in vitro models, we further characterized these fungal-bacterial interactions at the molecular level using C. albicans deletion mutant strains.