The use of molecular techniques for epidemiologic typing of Candida species

The availability of an epidemiologic typing system for Candida species that is sensitive, rapid, inexpensive, and easy to perform would clearly be an advantage to the mycologist, microbiologist, and epidemiologist in the ongoing struggle to understand the epidemiology and pathogenesis of candidiasis. This is particularly true given the increasing prominence of organisms such as C. albicans and C. tropicalis which are ubiquitous members of the normal flora yet are also important causes of nosocomial bloodstream infection. Unfortunately, the ideal epidemiologic typing system does not yet exist. Current data suggest that the molecular typing methods of restriction endonuclease digestion of genomic DNA with ethidium bromide staining (DEtBr typing) and electrophoretic karyotyping using pulsed-field electrophoresis offer rapid, simple, and sensitive means of discriminating strains of Candida species. These methods appear at present to be the most practical typing methods for both large- and small-scale epidemiologic studies. Other typing methods using specific DNA probes provide a powerful means of identifying strains and will undoubtedly be applied more broadly in the future. Thus far, studies employing molecular typing methods have documented that (1) most patients are colonized by one strain of Candida species, (2) isolates of Candida species recovered from blood or deep tissue sites are generally identical to those obtained from colonization sites before infection developed, and (3) nosocomial transmission of a single strain of C. albicans may occur, particularly in an intensive care unit setting. Given the limitations of the available typing methods and the complex nature of the patients at risk for candidiasis, both the epidemiologist and laboratory scientist must use these methods with clear epidemiologic objectives in mind. Whenever possible, all organisms to be typed should be typed by the same person on the same day, and typing should always include unrelated as well as epidemiologically related isolates. Additional studies, based upon sound epidemiologic principles, will be necessary to clarify the role of the various molecular typing methods as epidemiologic markers of Candida species and to further our understanding of the epidemiology and pathogenesis of candidiasis.