Time- lapse mesoscopy of Candida albicans and Staphylococcus aureus dual- species biofilms reveals a structural role for the hyphae of C. albicans in biofilm formation

Polymicrobial infection with Candida albicans and Staphylococcus aureus may result in a concomitant increase in virulence and resistance to antimicrobial drugs. This enhanced pathogenicity phenotype is mediated by numerous factors, including metabolic processes and direct interaction of S. aureus with C. albicans hyphae. The overall structure of biofilms is known to contribute to their recalcitrance to treatment, although the dynamics of direct interaction between species and how it contributes to pathogenicity is poorly understood. To address this, a novel time- lapse mesoscopic optical imaging method was developed to enable the formation of C. albicans/S. aureus whole dual- species biofilms to be followed. It was found that yeast- form or hyphal- form C. albicans in the biofilm founder population profoundly affects the structure of the biofilm as it matures. Different sub- populations of C. albicans and S. aureus arise within each biofilm as a result of the different C. albicans morphotypes, resulting in distinct sub- regions. These data reveal that C. albicans cell morphology is pivotal in the development of global biofilm architecture and the emergence of colony macrostructures and may temporally influence synergy in infection.