CLSI M44-A2 Disk Diffusion Test

EUROLAB, with its state-of-the-art accredited laboratories and expert team, provides precise and fast testing services within the scope of CLSI M44-A2 testing. This standard has recently been standardized by the CLSI and susceptibility breakpoints have been established for various antifungal compounds.

5 µg discs have been approved for caspofungin and 10 µg discs are under evaluation for micafungin. We evaluated the performances of the caspofungin and micafungin disc assay using a panel of Candida isolates with and without known FKS echinocandin resistance mechanisms.

Disk diffusion and microdilution experiments were performed strictly according to CLSI documents M44-A2 and M27-A3. Eighty-nine clinical Candida isolates were included: Candida albicans (20 isolates/10 mutants), C. glabrata (19 isolates/10 mutants), C. dubliniensis (2 isolates/1 mutant), C. krusei (16 isolates/3 mutants) ), C. parapsilosis (14 isolates/0 mutants) and C.tropicalis (18 isolates/4 mutants).

Quality control strains were C.parapsilosis ATCC 22019 and C. krusei ATCC 6258. Correlations between zone diameters and MIC results were good for both compounds, with identical susceptibility classifications for 93.3% of the isolates applying current CLSI breakpoints. However, the number of fks hot spot mutant isolates misclassified as susceptible (S) (very major errors [VMEs]) was high (11% for caspofungin [S, ≥61 mm] and 14% for micafungin [S, ≥93 mm]) ]). Changing the disc diffusion cutoff point to S at ≥22 mm significantly improved separation. 1 VME (a C.tropicalis isolate with an F76S substitution) (3.5%) was detected for caspofungin and 8 VMEs, mostly for C. glabrata (10/10), for micafungin.

The broadest distinction between zone diameter ranges for wild-type (WT) and mutant isolates was seen for caspofungin (6 to 12 mm versus -4 to 7 mm). In conclusion, the caspofungin disk diffusion test with a modified cutoff provided excellent discrimination between WT and mutant isolates for all Candida species.

EUROLAB assists manufacturers with CLSI M44-A2 test compliance. Our test experts, with their professional working mission and principles, provide you, our manufacturers and suppliers, the best service and controlled testing process in our laboratories. Thanks to these services, businesses receive more effective, high-performance and quality testing services and provide safe, fast and uninterrupted service to their customers.