Comparison of E Test and Disc Diffusion Methods for Susceptibility Testing of Filamentous Fungi; Experience of a Routine Lab

Abstract

Background: Testing for antifungal susceptibility to newly introduced drugs is standardized through the clinical laboratory standard institute (CLSI) broth micro-dilution method for testing of molds (M38-A2), yet is difficult to use routinely. Objectives: To compare two agar-based diffusion methods on two types of media for fungal drug sensitivity testing. Materials and Methods: The E-test method and the disc diffusion method were used on non-supplemented Muller Hinton agar (MHA) and RPMI for evaluating the in-vitro susceptibility of 48 clinical isolates of filamentous fungi to amphotericin B, itraconazole, voriconazole, and caspofungin. Results: Categorical agreement between E-test and disc diffusion method for itraconazole and voriconazole was 100%, yet for amphotericin B on MHA agar was 66.67%, and on RPMI, it was 47.92%. The correlation coefficient (R) between the inhibition zone diameters when using MHA and RPMI for itraconazole, voriconazole, amphotericin B and caspofungin was +0.745, +0.901 +0.649, and +0.409, respectively. Conclusions: Routine antifungal susceptibility testing using disk diffusion can be implemented in routine microbiology work up in limited resources.