Evaluation of Etest Performed in Mueller–Hinton Agar Supplemented with Glucose for Antifungal Susceptibility Testing of Clinical Isolates of Filamentous Fungi

Abstract

Although reference broth microdilution protocol is currently available for filamentous fungi antifungal susceptibility testing (AFST), simpler alternatives as Etest(®) tend to be favoured in clinical routine, making their validation of utmost importance. In this study, Etest(®) method using 2% glucose supplemented Muller-Hinton agar was compared to the Clinical and Laboratory Standards Institute (CLSI) M38-A2 protocol for filamentous fungi AFST. The echinocandins, caspofungin and anidulafungin, the azoles voriconazole and posaconazole, and the polyene amphotericin B were tested against 48 Aspergillus spp., seven Fusarium spp., one Beauveria bassiana and three Paecilomyces lilacinus isolates. The majority of the isolates were susceptible to the antifungals tested, and the overall level of agreement between the CLSI and Etest methods was 71.9% for one dilution and 99.7% when using two dilutions. Since interpretative breakpoints for filamentous fungi employing the CLSI or Etest methods are not available yet, the established epidemiological cut-off values for Aspergillus spp. were used to distinguish wild-type isolates from those with acquired resistance mechanisms. Forty-five Aspergillus strains did not evidence resistance mutations.

Antifungal Susceptibly Testing by Concentration Gradient Strip Etest Method for Fungal Isolates: A Review

“…(20 isolates) reported an 85% EA with CLSI MICs [63]. When testing the echinocandins, which exhibited no in vitro activity against Fusarium spp., a 100% agreement was found between Etest caspofungin, micafungin, and anidulafungin and CLSI MICs [66,68,74]. Overall, the Etest could to be a good alternative method for testing of Fusarium spp., but unusually high MICs should be confirmed by the CLSI method since ECVs for some of these species only are available by this method.…”

“…As for amphotericin B MICs, Etest itraconazole MICs were usually higher than CLSI values [60,65,67,69,76,78,87]. In contrast, Etest voriconazole, posaconazole, and isavuconazole MICs were generally lower than CLSI endpoints [57,58,61,63,66,72,74,87].…”

“…Echinocandin MICs by the Etest have been evaluated in several studies, mainly for caspofungin [23,62,66,68,74,78] and to a lesser extent for micafungin [66,68,78] and anidulafungin [68,74,78]. EA was generally good (up to 100%), but lower values also have been reported in some of the studies (Table 5).…”

Subcutaneous infection by Ochroconis mirabilis in an immunocompetent patient

“…The in vitro susceptibility of the strain to eight antifungal agents was determined using the microdilution method in accord with the guidelines of the Clinical and Laboratory Standards Institute (CLSI) M38A at day +28 [11] . The minimum inhibitory concentrations (MICs) were defined as the lowest concentration at which no growth occurred which led to the following results: itraconazole 4 μg/ml; ketoconazole, >8 μg/ml; fluconazole, >64 μg/ml; miconazole 2 μg/ml; voriconazole 2 μg/ml; anidulafungin, >4 μg/ml; amphotericin B, >4 μg/ml and terbinafine 0.06 μg/ml.…”

Chromoblastomycosis due to Fonsecaea monophora misdiagnosed as sporotrichosis and cutaneous tuberculosis in a pulmonary tuberculosis patient

“…At day +10, the in vitro susceptibility of the strain to eight antifungal agents was determined using the microdilution method in accordance with the guidelines of the Clinical and Laboratory Standards Institute (CLSI) M38A [4] . The minimum inhibitory concentrations (MICs) were defined as the lowest concentration at which no growth occurred which led to the following results: itraconazole, 0.06 μg/ml; ketoconazole, 0.5 μg/ml; fluconazole, 16 μg/ml; miconazole, 2 μg/ml; voriconazole, 0.06 μg/ml; anidulafungin, >4 μg/ml; amphotericin B, 16 μg/ml; terbinafine, 0.06 μg/ml.…”