(157c) Understanding Candida Albicans and Candida Glabrata Mixed Species Biofilm Growth and Co-Culture

Candidiasis, fungal infection caused by Candida species, affects patients of all ages and ranges from thrush in the oral cavity to disseminated deep tissue infections. Candida infections may be difficult to treat due to inherent or acquired antifungal resistance, and limited number of available therapeutic agents; with immunocompromised patients being the largest at-risk population. Biofilms, which are often associated with the pathogenesis of Candida, are generally polymicrobial in nature, and are held together by an extracellular matrix (ECM) that is attached to a surface.  In the human host, this surface may by a catheter, mucosal surface of the gastrointestinal tract, or lining of the stomach. Biofilms are difficult to treat largely due to the protective ECM, which reduces the penetration and efficacy of antifungal agents.  C. albicans and C. glabrata are the two most commonly isolated species from Candida infections, and have been isolated together, which makes polymicrobial populations an interesting and clinically relevant area of study.  In this work, we characterize the impacts of co-cultures in biofilm formation and population dynamics using mixed cultures of C. albicans and C. glabrata.  When grown as biofilms, we find that biofilm formation of the polymicrobial population depends on the relative ratio of starting cell concentrations of C. albicans and C. glabrata in an unexpected manner.  The specific ratio we find to yield the highest biomass is when the ratio of C. albicans to C. glabrata is low.  C. glabrata, in comparison to C. albicans, is not very successful at forming biofilms when grown as a single species. Interestingly, we find that the higher ratios of C. albicans to C. glabrata in fact result in less biofilm formation than the low C. albicans to C. glabrata counterpart. When co-cultured in liquid medium in suspension, one of the species consistently exhibits a growth advantage over the other.   Our results suggest interspecific interactions between these two fungal pathogens, where a polymicrobial population causes unexpected changes in biofilm formation.  The underlying mechanisms of these inter-specific interactions are being investigated.