Clinical Implications of Oral Candidiasis: Host Tissue Damage and Disseminated Bacterial Disease

The clinical significance of polymicrobial interactions, particularly those between commensal species with high pathogenic po-tential, remains largely understudied. Although the dimorphic fungal species Candida albicans and the bacterium Staphylococ-cus aureus are common cocolonizers of humans, they are considered leading opportunistic pathogens. Oral candidiasis specifi-cally, characterized by hyphal invasion of oral mucosal tissue, is the most common opportunistic infection in HIV and immunocompromised individuals. In this study, building on our previous findings, a mouse model was developed to investigate whether the onset of oral candidiasis predisposes the host to secondary staphylococcal infection. The findings demonstrated that in mice with oral candidiasis, subsequent exposure to S. aureus resulted in systemic bacterial infection with high morbidity and mortality. Histopathology and scanning electron microscopy of tongue tissue frommoribund animals revealed massive C. albi-cans hyphal invasion coupled with S. aureus deep tissue infiltration. The crucial role of hyphae in the process was demonstrated using a non-hypha-producing and a noninvasive hypha-producing mutant strains of C. albicans. Further, in contrast to previ-ous findings, S. aureus dissemination was aided but not contingent upon the presence of the Als3p hypha-specific adhesion. Im-portantly, impeding development of mucosal C. albicans infection by administering antifungal fluconazole therapy protected the animals from systemic bacterial disease. The combined findings from this study demonstrate that oral candidiasis may con