Laboratory diagnosis of systemic fungal diseases.

The increase in the number of fungal infections seen in debilitated and immunocompromised patients in the last several years makes it necessary to consider all fungi as potential pathogens. Clinical microbiology laboratories are playing increasingly important roles in the recovery, isolation, and identification of these fungi. This article contains specific recommendations and references concerning a practical approach to the laboratory identification of systemic fungi. The proper and timely selection, collection, and transport of specimens is imperative, and clinicians are responsible for appropriate specimen selection to ensure optimal chances of recovery of pathogens. Respiratory tract secretions and blood are excellent sources for detection of disseminated fungal infection. Specimens should be placed into transport media if the sample size is small or if only a small number of organisms are thought to be present. Direct microscopic examination of specimens can provide valuable information, often allowing a clinician to initiate immediate therapy. Specimens that are more likely than others to contain systemic fungi and that should be examined routinely include the following: pulmonary biopsy material, bronchial washes and lavages, specimens from immunocompromised patients, purulent specimens, and specimens suspected of containing a specific fungus. Valuable methods of examining specimens directly include treatment with KOH and calcofluor white. Use of media to recover fungi is the basis of making a laboratory diagnosis of a fungal disease, and the use of proper recovery and subculture media is imperative. Noninhibitory media allow contaminants to grow readily and should be used only to recover fungi from normally sterile body sites or for subculture. Blood-enriched media allow almost all pathogenic and saprophytic fungi to flourish. Therefore, such media, unless they contain antibiotics, should not be used as primary recovery media. Media that contain antibiotics should be used as primary recovery media to prevent overgrowth of pathogenic fungi by contaminants. Yeasts recovered from clinical specimens can be identified by a combination of tests, which include direct microscopic examination, germ tube formation, microscopic morphology of growth on corn meal agar, and ability to utilize certain carbohydrates. Molds recovered from clinical specimens are identified by a combination of growth rate, colonial characteristics, size and shape of hyphae, and microscopic examination of reproductive structures and other fungal elements.(ABSTRACT TRUNCATED AT 400 WORDS)