Candida,Cryptococcus, and Other Yeasts of Medical Importance

Abstract

The taxonomy of yeasts is continually evolving, and currently yeasts that are of medical importance belong to two classes: the Saccharomycetes (previously Hemiascomycetes or Endomycetes), which contains Candida species, and the Tremellomycetes (previously Heterobasidiomycetes), which contains the basidiomycetous fungi Trichosporon and Cryptococcus. A number of species have been merged into Candida albicans, including Candida claussenii and Candida langeronii. There is evidence that C. albicans var. africana may be a new cause of vaginitis that is often misidentified as C. albicans on the Vitek 2 ID-YST system. Candida species are ubiquitous yeasts, being found on many plants and as the normal biota of the alimentary tract of mammals and mucocutaneous membranes of humans. In nearly 45% of AIDS patients, cryptococcosis was reported as the first AIDS-defining illness. Because none of the presenting signs or symptoms of cryptococcal meningitis (such as headache, fever, and malaise) are sufficiently characteristic to distinguish it from other infections that occur in patients with AIDS, determining cryptococcal antigen titers and culturing blood and cerebrospinal fluid (CSF) are useful in making a diagnosis. Not surprisingly, little effort has been undertaken to develop serologic tests for detection of invasive infections caused by yeasts other than Candida and Cryptococcus species. In order to develop a universal genetic identification system for yeasts, the most reproducible, specific, and sensitive sequence for comparison must be identified, and the majority of research has focused on the rDNA regions.