AGAR-BASED SCREENING FOR AZOLE RESISTANCE IN ASPERGILLUS FUMIGATUS USING VIPcheck™: A SINGLE CENTRE EVALUATION [PublishAheadOfPrint]

Introduction Antifungal susceptibility testing is an essential tool for guiding therapy, although EUCAST and CLSI reference methods are often only available in specialized centres. We studied the performance of an agar-based screening method for the detection of azole resistance in Aspergillus fumigatus cultures.

Methods The VIPcheck™ consists of four wells containing voriconazole, itraconazole, posaconazole or a growth control. Ninety-six A. fumigatus isolates were used. Thirty-three isolates harboured a known resistance mechanism: TR₃₄/L98H (11 isolates); TR₄₆/Y121F/T289A (6 isolates); TR₅₃ (2 isolates) and fourteen isolates with other cyp51A-gene point mutations. Eighteen resistant isolates had no cyp51A-mediated azole resistance. 45 isolates had a wild type (WT) azole phenotype. Four technicians and two inexperienced interns, blinded to the geno/phenotype, read the plates visually after 24h and 48h and documented minimal growth, uninhibited growth and no growth. The performance was compared to the EUCAST method.

Results After 24h incubation the mean sensitivity and specificity were 0.54 and 1.00 with uninhibited growth as threshold. After 48h incubation the performance mean sensitivity/specificity were 0.98 and 0.93 with minimal growth. The performance was not affected by experience in mycology. The interclass correlation coefficient was 0.87 after 24h and 0.85 after 48h.

Conclusion VIPcheck™ enabled selection of azole-resistant A. fumigatus colonies with a mean sensitivity and specificity of 0.98 and 0.93. Uninhibited growth on any azole-containing well after 24h and minimal growth after 48h were indicative of resistance. These results indicate that the VIPcheck™ is an easy-to-use tool for azole resistance screening and selection of colonies that require MIC-testing.

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