Candida Albicans
Candida species. are normal flora found in the gastrointestinal tract, mucous membranes, and skin. Invasive candidiasis is typically an opportunistic infection with the patient’s own, endogenous flora. Although it can be normal skin flora, the growth of Candida species from a blood culture should be presumed to be pathogenic; treatment should be initiated, and attempts made to identify the source. Typically, invasive candidiasis arises from one of three sources:
- Colonization and biofilm formation on an indwelling intravenous catheter
- Dissemination from a deep nidus of infection, often urinary tract
- Translocation from the gastrointestinal tract.
Patients in intensive care, those who are immunocompromised, at extremes of age, those who have been on broad spectrum antibiotics, and those with GI tract perforation or anastamotic leaks post-operatively are at greatest risk for developing invasive candidiasis.
C. albicans has historically been the most common species of yeast causing invasive disease. However, non-albicans species (C. glabrata, C. parapsilosis, C. tropicalis and C. krusei) now cause almost 50% of invasive candidiasis. This changing epidemiology is relevant because the different species demonstrate different susceptibility profiles to antifungal agents, including azoles and echinocandins. C. aurisis another recently emerging species that shows resistance to multiple antifungal agents, and has been described as causing outbreaks of healthcare-associated infections.
Candida species are the most common yeast cultured from clinical specimens. Candida albicans is characterized macroscopically by growth of smooth, white colonies with surrounding “feet” which represent projections of pseudohyphae. The pseudohyphae are distinguished microscopically from true hyphae by constriction of the cells where they meet (with true hyphae, the cell walls will remain parallel). When incubated at 37 C for 2 hours. C. albicans will produce germ tubes (extensions from the yeast cell representing an attempt at forming true hyphae).
