Commensal to Pathogen Transition of Candida albicans.
The yeast Candida albicans is an archetypical opportunistic pathogen. This fungus commonly occurs as a commensal on mucosal surfaces of humans but causes infections under certain circumstances. Namely, if epithelial barriers are disturbed or the immune system is impaired. Infections can be superficial, affecting only the mucosal tissue, or life-threatening if the fungus disseminates. The main reservoir of C. albicans is the gut, where it has to adapt to changes in pH, oxygen, and nutrient availability, and competes with other microbes. For the transition from commensalism to pathogenesis, the fungus uses distinct mechanisms that facilitate adherence to and invasion of host cells. Following dissemination, the environmental conditions change and additionally, C. albicans has to avoid elimination by humoral and cellular components of the immune system. Fungal factors and signaling networks mediate the adaptation to these different situations. While some are specific for either commensalism or disseminated disease, other attributes contribute to both the commensal and pathogenic lifestyle of this fungus. In this reference module we summarize the current knowledge on the features that contribute to C. albicans being a successful and harmless colonizer of the human gut and on the transition to a pathogen.