[Comparison of the results of in vitro antifungal susceptibility testing using the Fungitest kit and the disc diffusion test].

AIM OF STUDY

Substantial progress has been achieved in the field of in vitro antifungal susceptibility testing, including the interpretation of the test results towards the clinical practice. Reference methods for antifungal testing of yeasts (M27-A) and filamentous fungi (M38-P) are available now. There are several alternatives to these standard protocols as the potential candidates for a routine laboratory testing of antifungal drugs. The aim of the study is to compare the results of antifungal susceptibility testing obtained by Fungitest and disk diffusion method.

MATERIALS AND METHODS

From 1997 to 2000, 134 strains of 16 yeast species from the patients with suspected or proven mycosis were evaluated in the mycology laboratory of the Department of Clinical Microbiology, Teaching Hospital in Hradec Krlové. All these strains were tested by both disc test on Sabouraud agar (pH = 5.6) and Fungitest. The agreement of the results of the both methods was determined for all antimycotics and fungal species tested in terms of the categories susceptible, intermediate and resistant strain.

RESULTS

Overall, there was only 60.3 % agreement between these methods for all antifungal drugs with the best results for flucytosine (71.4 % agreement), further for ketoconazole (66.2 %), amphotericin B (60.2 %), fluconazole (57.9 %), itraconazole (52.6 %), and miconazole (50.5 %). The best overall agreement between the results for individual species was found with C. lusitaniae (73.9 %), C. pelliculosa (73.5 %), C. parapsilosis (71.7 %), and partly with C. albicans (67.5 %). The poorest results were associated with fluconazole-resistant yeasts Saccharomyces cerevisiae (30.0 %), C. krusei (32.5 %) and C. glabrata (47.7 %). Regressive analysis revealed a relative close relationship between the results of these methods for miconazole (R = 0.49, P < 0.001), fluconazole (R = 0.45, P < 0.001), itraconazole (R = 0.42, P < 0.001) and flucytosine (R= 0.37, P < 0.001), but not for amphotericin B (R = 0.10) and ketoconazole (R = 0.16).

CONCLUSION

The comparison of the results of the disk test and Fungitest showed some discrepancies which were dependent on an antifungal drug, a yeast species and the test conditions. Sabouraud agar and the criteria for interpretation of the results of the disk test seemed to be main sources of the disagreement. A modified Mueller-Hinton agar (2 % glucose, methylene blue) as a recommended test medium in a proposed agar diffusion method M44-P is the way to the improvement of standardization and reproducibility of the test.