Candida albicansenhanceStaphylococcus aureusvirulence by progressive generation of new phenotypes

Candida albicans and Staphylococcus aureus have been co-isolated from several biofilm- associated diseases, including those related to medical devices. This association confers advantages to both microorganisms, resulting in detrimental effects on the host. To elucidate this phenomenon, the present study investigated colony changes derived from non-physical interactions between C. albicans and S. aureus . We performed proximity assays by confronting colonies of the yeast and the bacteria on agar plates at six different distances for 9 days. We found that colony variants of S. aureus originated progressively after prolonged exposure to C. albicans proximity, specifically in response to pH neutralization of the media by the fungi. The new phenotypes of S. aureus were more virulent in a Galleria mellonella larvae model compared to colonies grown without C. albicans influence. This event was associated with an upregulation of RNAIII and AgrA expression, suggesting a role for α-toxin. Our findings indicate that C. albicans enhances S. aureus virulence by inducing the formation of more aggressive colonies. Importance For decades, it has been known that C. albicans increase S. aureus virulence, resulting in a “lethal synergism”. However, it was only recently identified that this outcome is driven by the sustained activation of the staphylococcal agr system in response to C. albicans environmental modifications. Our experimental design allowed us to observe individual changes over time caused by the proximity of both microorganisms. As a result, we report for first time that C. albicans exposure induces the generation and favors the growth of S. aureus colony variants with increased expression of virulence factors. Our findings highlight the importance to understanding the intricate connection between environmental responses, virulence and fitness in S. aureus pathogenesis.