Evaluation of fluorescence in situ hybridisation (FISH) for the identification of Candida albicans in comparison with three phenotypic methods

Severe Candida infections are increasing and are associated with considerable morbidity and mortality. Rapid and accurate differentiation of Candida albicans from non-C. albicans species is essential for therapeutic decisions. We therefore developed a fluorescence in situ hybridisation (FISH) assay comprising previously described probes and a newly designed specific C. albicans probe/competitor probe combination. The FISH probes were first evaluated using 99 selected fungal strains covering 31 species, and a specificity between 96% and 100% and a sensitivity of 100%. The FISH assay was then applied to 110 clinical isolates in parallel with API32C, the chromogenic Candida ID agar, and determination of filamentous colony morphology. All tests produced highly reliable results. However, the Candida ID agar misidentified Candida dubliniensis as C. albicans. Determination of filamentous colony morphology allowed 100% reliable identification of C. albicans, but took 48 h. FISH allowed identification of clinical C. albicans isolates within 3 h with a sensitivity and specificity of 100%. FISH was additionally applied to 48 blood cultures showing yeasts in the Gram stain and correctly identified all 33 cases of C. albicans.