Oral colonization by Candida albicans

Candida albicans is a commensal yeast normally present in small numbers in the oral flora of a large proportion of humans. Colonization of the oral cavity by C. albicans involves the acquisition and maintenance of a stable yeast population. Micro-organisms are continually being removed from the oral cavity by host clearance mechanisms, and so, in order to survive and inhabit this eco-system, C. albicans cells have to adhere and replicate. The oral cavity presents many niches for C. albicans colonization, and the yeast is able to adhere to a plethora of ligands. These include epithelial and bacterial cell-surface molecules, extracellular matrix proteins, and dental acrylic. In addition, saliva molecules, including basic proline-rich proteins, adsorbed to many oral surfaces promote C. albicans adherence. Several adhesins present in the C. albicans cell wall have now been partially characterized. Adherence involves lectin, protein-protein, and hydrophobic interactions. As C. albicans cells evade host defenses and colonize new environments by penetrating tissues, they are exposed to new adherence receptors and respond by expressing alternative adhesins. The relatively small number of commensal Candida cells in the oral flora raises the possibility that strategies can be devised to prevent oral colonization and infection. However, the variety of oral niches and the complex adherence mechanisms of the yeast mean that such a goal will remain elusive until more is known about the contribution of each mechanism to colonization.