Candida albicans and Staphylococcus aureus reciprocally promote their virulence factor secretion and pro-inflammatory effects.

Background: Co-infections of Candida albicans and Staphylococcus aureus can significantly increase morbidity and mortality. However, the effect of C. albicans-S. aureus co-existence on virulence factor secretion and pro-inflammatory effects remain elusive.
Methods: We systematically investigated the virulence factors released by C. albicans and S. aureus under different culturing conditions using proteomics. We characterized their pro-inflammatory effects in macrophages with transcriptomics and gene set enrichment analysis.
Results and Discussion: We showed that co-culturing of C. albicans and S. aureus promoted the secretion of 7 cytolytic, 11 proteolytic, and 3 lipolytic extracellular virulence factors (ECVFs) and impacted non-ECVFs, owing to Als1/Als3-mediated interactions, the presence of C. albicans, or its pH maintenance. Co-culturing promotes C. albicans hypha formation and β-glucan masking, suggesting that co-culturing enhances both C. albicans invasion and immune evasion. Moreover, the secretome of C. albicans-S. aureus co-culture increased pro-inflammatory pathways including promoting TNF-, NFKB-, and Toll-like receptor signaling pathways, as well as cytokine-cytokine receptor interactions in macrophages. Our findings support that C. albicans and S. aureus reciprocally promote their virulence potential and pro-inflammatory effects, which may provide mechanistic insights into the increased morbidity and mortality during their co-infection in vivo.