Tipping the Balance: C. albicans Adaptation in Polymicrobial Environments

Abstract

Candida albicans is a pleiomorphic fungus which co-exists with commensal bacteria in mucosal and skin sites of mammalian hosts. It is also a major co-isolated organism from polymicrobial systemic infections, with high potential for morbidity or mortality in immunocompromised patients. Traditionally, resident mucosal bacteria have been thought to antagonize C. albicans in its ability to colonize or cause infection. However, recent investigations have revealed synergistic relationships with certain bacterial species that colonize the same mucosal sites with C. albicans. Such relationships broaden the research landscape in pathogenesis but also contribute to clinical challenges in the prevention or treatment of mucosal candidiasis. This review sheds light on interactions of C. albicans and mucosal bacteria, with special emphasis on the effects of the resident bacterial microbiota on C. albicans physiology as they relate to its adaptation in mucosal sites as a commensal colonizer or as a pathogenic organism.

Keywords: Candida albicans; candidiasis; fungal-bacterial interactions; polymicrobial interactions.

Figure 1

Relationship between C. albicans and resident mucosal bacteria in heath and disease: Immunosuppression is associated with a dysbiotic state characterized by overgrowth of Candida and certain resident bacterial species. Bacteria may interact with Candida species to augment the mucosal inflammatory response, resulting in epithelial damage. Alternatively, bacteria can directly influence filamentation and virulence gene expression to increase mucosal invasion. PRR: pattern recognition receptors; TLR: toll-like receptors; NOD: nucleotide-oligomerization domain.