Antifungal susceptibility of the aspergillus species by Etest and CLSI reference methods

Because resistance to antifungal drugs is seen in patients, susceptibility testing of these drugs aids in choosing the appropriate drug and respective epidemiology. This study has investigated and compared susceptibility patterns of the Aspergillus species isolated from patients by the Clinical and Laboratory Standards Institute (CLSI) reference broth microdilution (MD) assay and Etest method.

The minimum inhibitory concentrations (MICs) of various antifungal agents (amphotericin B, ketoconazole, itraconazole, and voriconazole) for 108 Aspergillus species isolated from patients were determined by CLSI M38-A broth MD and Etest. The isolates were obtained from clinical samples that included tissues, sputum, bronchoalveolar lavage, abdominal tap, and cerebrospinal fluid.

As revealed by the MD method, 63.9% of the isolates were sensitive to amphotericin B and 36.1% were resistant.Etest revealed that 61.1% were sensitive to amphotericin B and 38.9% were resistant. As for ketoconazole, 108 isolates (100%) were shown to be sensitive through the MD method; while the Etest revealedan 88.9% sensitivity and 11.1% were resistant. All species were susceptible to voriconazole, according to both methods. The measure of agreement (Kappa Index) for these three drugs was satisfactory (≥0.6). According to the MD method, 69.4% of the species were susceptible to itraconazole, whereas 30.6% were not.For this drug, the Etest showed 86.1% susceptible and 13.9% resistant.

Voriconazole was the most effective agent against isolates. Using RPMI agar, we found the Etest to be helpful, readily available, and easy to use for determining invitro susceptibilities of Aspergillus species to voriconazole, amphotericin B, ketoconazole, and itraconazole in the region of this study.