Modification of antifungal susceptibility testing for Aspergillus species

Abstract

Background: In resource constrained laboratories, determination of antifungal susceptibility as described by CLSI and EUCAST guidelines is not always feasible. So, we have modified the method of Antifungal susceptibility testing (broth microdilution method) done for Aspergillus sp. to see whether the MIC values obtained are comparable with that of CLSI and EUCAST methods.Methods: MICs for 30 isolates of Aspergillus sp. were determined against locally available drugs like amphotericin B injection (diluent-distilled water) and itraconazole granules (diluent-Dimethyl sulfoxide). SDA broth (pH 7) and RPMI 1640 are used as test medium. Broth microdilution method was followed and MICs were read at 48hrs, compared with references in CLSI and EUCAST standards.  Minimum inhibitory concentration is taken as 100% inhibition of growth visually.Result: MIC ranges observed for amphotericin B in µg/ml for A.flavus(8) is 0.5-1, A.fumigatus(6) 0.25-0.5, A.niger(10) 0.5-1, A.terreus(6) 0.5-1. Similarly  MIC ranges for itraconazole are A.flavus(8)  0.5-1, A.fumigatus(6) 0.5-1, A.niger(10) 0.25-2, A.terreus(6) 0.5-1.Control strains were kept to check the quality control. These ranges are comparable to CLSI and EUCAST standards.Conclusion: MIC ranges obtained in the study are within the ranges as published by CLSI and EUCAST guidelines. The   observations  in this pilot study will help for extending the method on larger number of isolates of filamentous fungi for standardisation.