Antifungal drug susceptibility testing of Candida sp. by two methods: CLSI(M27-A2) broth microdilution and the image analyser method Wider-I

Abstract number: 1733_1461

Rodriguez-Dominguez M., Ayala G., Fernandez-Olmos A., Mercadillo M., Alvarez M., Sanchez-Sousa A., Espinel-Ingroff A.

Introduction: Accurate as well as faster methods than CLSI methodology are needed for in vitro susceptibility testing of yeasts. WIDER I (Francisco Soria Melguizo S.A., Madrid, Spain) is a less labour-intensive and much simpler to perform assay than the CLSI broth microdilution M27-A2 method. Wider I is a computer-assisted image processing system, optimised for microdilution susceptibility testing of yeasts.

Objectives: To evaluate the suitability of the WIDER I system for testing the in vitro susceptibility of Candida spp. to four antifungal agents. We compared results by this automated method to those by the CLSI reference method for yeasts (M27-A2 document).

Methods: We tested 101 yeasts isolates from transplant recipients (C. albicans 71, C. glabrata 13, C. parapsilosis 8, C. lusitaniae 4, C. krusei 2, C. famata 1, C. guilliermondii 1, C. tropicalis 1) against amphotericin B, voriconazole, itraconazole and fluconazole with both CLSI (M27-A2) and WIDER I methods.

Results: Agreement (within three dilutions) between methods for voriconazole and fluconazole was 90% and 87%, respectively 74% for itraconazole. For amphotericin B, the agreement between both methods was excellent at 24 h (97%). By breakpoint category, the agreement was 91% for fluconazole (VME = 1% [very major errors, susceptible by new method and resistant by reference method], ME = 3% [major errors, resistant by new method and susceptible by reference method] and M = 5% [minor errors, shifting between categories]. The agreement by category was 93% for voriconazole (ME = 5%, M = 2%) and lower (87.1%) for itraconazole (VME = 3%, ME = 1% and M = 8.9%).

Conclusion: Although MIC results varied between the methods, we found a high level of agreement by breakpoint categories. Further evaluations are needed to assess the suitability of this method.