Effects of culture media on the in vitro susceptibility of selected opportunistic fungi to fluconazole and itraconazole.

The sensitivity of 23 isolates of opportunistic fungi, Aspergillus fumigatus (5), A. flavus (5), A. niger (5), Pseudallescheria boydii (5), Alternaria alternata (2) and Xylohypha bantiana (1), was investigated against fluconazole and itraconazole, using Sabouraud's dextrose broth (SD) and a high-resolution (HR) medium (Pfizer, Inc.). The procedure followed was a standard tube dilution (1 ml/tube) method. Candida albicans Y01 09 was included as reference strain to monitor quality and reproducibility. Results indicated that the minimal inhibitory concentrations (MICs) of fluconazole for all Aspergillus spp. and C. albicans were greater than or equal to 100 micrograms/ml in SD medium, whereas, for P. boydi, A. alternata and X. bantiana, the MICs were 50 micrograms/l. The MICs of itraconazole in SD medium were less than 0.195-1.56 micrograms/ml for the fungi tested. In HR medium, the MICs of fluconazole for the Aspergillus spp, were greater than or equal to 100 micrograms/ml, and those for P. boydii, A. alternata and X. bantiana were 0.78, 50 and 50 micrograms/ml, respectively. The MICs of itraconazole for all fungi ranged from less than 0.198 to 0.78 micrograms/ml in the HR medium. The values for the reference strain were 1.56 and 100 micrograms/ml in the HR medium for fluconazole and itraconazole, respectively. The HR medium was more suitable for testing P. boydii against fluconazole. This culture medium did not appear to significantly affect the MICs of itraconazole as compared to those of fluconazole, for the fungi investigated.