Relative abundance of Candida albicans and Candida glabrata in in vitro co-culture biofilms impacts biofilm structure and formation

Michelle L. Olson (1), Arul Jayaraman (1), Katy C. Kao (1)

1. Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX, 77843

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Candida is a member of the normal human microbiota and often resides on mucosal surfaces such as the oral cavity or the gastrointestinal tract. In addition to their commensality, Candida species can opportunistically become pathogenic if the host microbiota is disrupted or if the host immune system becomes compromised. An important factor for Candida pathogenesis is its ability to form biofilm communities. The two most medically important species - Candida albicans and Candida glabrata - are often co-isolated from infection sites, suggesting the importance of Candida co-culture biofilms. In this work, we report that biofilm formation of the co-culture population depends on the relative ratio of starting cell concentrations of C. albicans (Ca) and C. glabrata (Cg). When using a starting ratio of Ca:Cg of 1:3, a ~6.5- and ~2.5-fold increase in biofilm biomass was observed relative to Ca monoculture and a Ca:Cg ratio of 1:1, respectively. Confocal microscopy analysis revealed heterogeneity and complex structures composed of long Ca hyphae and Cg cell clusters in the co-culture biofilms, and qRT-PCR studies showed an increase in the relative expression of the HWP1 and ALS3 adhesion genes in the Ca:Cg 1:3 biofilm compared to Ca monoculture biofilm. Additionally, only the 1:3 Ca:Cg biofilm demonstrated increased resistance to the antifungal drug caspofungin. Overall, the results suggest that interspecific interactions between these two fungal pathogens increase biofilm formation and virulence-related gene expression in a co-culture composition-dependent manner.

Keywords: Candida, biofilms, co-culture, CLSM

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