Recent advances for the routine mycology laboratory

Abstract number: S70

Arendrup M.

Successful management of invasive fungal infections depends on timely and correct treatment. Over the last decades a number of new tests have become available which have improved the diagnostic options.

In contrast to the scenario for bacterial infections, acquired resistance in fungi is rare and thus species identification is a valuable tool guiding choice of treatment. Therefore, microscopy & culture is still a corner stone in diagnosis, but culture and identification are time consuming (app. 1–5 and 1–3 days, respectively).

The sensitivity and speed of microscopy have been improved by the use of fluorescent brighteners such as calcofluor white or blankophor. But only with the recent development of PNA probes specific for a number of the Candida spp. has species identification become possible directly from a positive blood culture before subculture on agar media.

Chromogenic agars allow a presumptive identification of several Candida spp. and facilitate the recognition of yeast isolates in samples containing several yeasts or yeast and bacteria in combination. The use of such plates has been shown to lead to a better identification of mixed cultures in a recent Nordic EQA scheme including more than 50 laboratories.

Rapid species identification of the most important Candida spp. is possible in the routine laboratory using easy commercially available kits. Thus, a species identification of C. albicans, C. dubliniensis and C. krusei can be obtained within minutes using latex agglutination kits (BICHRO-DUBLI, KRUSEI-COLOR; Fumouze Diagnostics) and C. glabrata can be rapidly identified due to its high amounts of preformed intracellular trehalase enzyme (Glabrata RTT; Fumouze Diagnostics). Finally, PNA probes and fluorescence microscopy can also be used for a same day identification of a range of the clinically relevant Candida spp. (AdvanDx).

Susceptibility testing is possible using Etest and the results are comparable with those obtained by reference methodologies in head to head comparisons. However, recent data from EQA distributions suggest that detection of isolates with acquired resistance causes many laboratories difficulties. This illustrates that a critical number of isolates should be tested per technician per week and quality control strains should be included on a regular basis.

In conclusion, a number of new diagnostic tests have become available over the last decade and the diagnostic laboratories are encouraged to take advantage of these new options.