Laboratory Diagnosis of Fungal Infections: An Overview

Abstract

With the increasing rate of fungal infection, it is important for clinical mycologists to know the details of classical and newer molecular approaches in diagnosis of fungal infection. The classical approach includes appropriate specimen collection and transport, as fungus isolation is not so easy as for bacteriological samples. Direct microscopic examination with 10% KOH and Calcofluor white staining plays a very important role, as it helps to provide a presumptive diagnosis to the physician and also permits the selection of appropriate culture media. The fungal culture media used are always two, one being a non-selective medium and the other with addition of antibiotics and cycloheximide, thus reducing bacterial and saprobic fungal contamination. To obtain a better fungal morphology, slide culture is usually done. There are certain differential test media to identify the different species of fungi. As the media for culture are available in plates or tubes, with their respective advantages and disadvantages, their use depends on the preference of the laboratory concerned. As we all know that fungi causing disease are either yeasts, molds or dimorphic, hence the culture media is incubated at two different temperatures of 30°C (for the mold form of all fungi) and 35°C (for yeast forms of dimorphic fungi). As it takes a long time for fungi to grow, they should be incubated for at least 30 days before giving a negative culture report. Fungal serology is currently performed only in selected reference laboratories. The test is rapid, and aids in diagnosis of systemic fungal infection, and also helps in the study of epidemiology of the fungal infection. The commonly used serological tests are ELISA, EIA, immunodiffusion and latex agglutination test, with commercially available kits. Now with the advent of molecular techniques including PCR and DNA probes, identification of fungal infection has become even more sensitive and specific. It is rapid, and can detect fungi even in culture plates contaminated with bacteria or other saprobic fungi. In this review, we will describe in detail the important clinical aspects in the laboratory diagnosis of fungal infections, and hope that it will be a reference chapter for beginners as well as for established researchers working in the current field.