Spectrophotometric MICs reading of azoles and amphotericin B shows high agreement with visual reading MIC interpretation using EUCAST 9.3.1 methodology

Julia Serrano Lobo 1, Pilar Escribano 1, Judith Diaz-Garcia 1, Waldo Sanchez-Yebra Romera 2, Leyre Lopez Soria 3, Miguel Fajardo 4, Belen Lorenzo 5, Ferrán Sánchez Reus 6, Inmaculada Vidal Catala 7, Marina Fernandez Torres 8, Isabel Sanchez-Romero 9, CarlosRuiz De Alegría-Puig 10, Jose Luis Del Pozo 11, Patricia Munoz 1, Jesus Guinea Ortega *1

Author address: 

1 Hospital General Universitario Gregorio Marañon, Madrid, Spain; 2 Complejo Hospitalario Torrecárdenas, Almería, Spain; 3 Hospital de Cruces, Bilbao, Spain; 4 Hospital Universitario de Badajoz, Badajoz, Spain; 5 Hospital Río Hortega, Valladolid, Spain; 6 Santa Creu y Sant Pau, Barcelona, Spain; 7 Hospital General de Alicante, Alicante, Spain; 8 Hospital Txagorritxu, Vitoria, Spain; 9 Hospital Puerta de Hierro, Madrid, Spain; 10 Hospital de Valdecilla, Santander, Spain; 11 Clínica Universitaria de Navarra, Pamplona, Spain


Background: EUCAST 9.3.1 procedure recommends visual MIC reading (complete fungal growth inhibition) with azoles and amphotericin B against Aspergillus spp. As visual MIC setting may be challenging, we obtained spectrophotometric MICs readings of azoles and amphotericin B against A. fumigatus complex isolates and compared them with visual method to overcome subjectivity.

Materials/methods: A total of 848 A. fumigatus complex clinical isolates collected in a 30-hospital survey conducted in Spain were studied. A. fumigatus sensu stricto isolates included 45 azole-resistant isolates with the following cyp51A gene mutations: TR34-L98H (n=24), G54R (n=5), TR46/Y121F/T289A (n=1), F46Y/M172V/N248T/D255E/E427K (n=2), F46Y/M172V/ N248T/D255E/E416Q/E427K (n=1), F165L (n=1), S496L (n=1), and wild type (n=10). Antifungal susceptibility to amphotericin B, itraconazole, voriconazole, posaconazole, and isavuconazole was performed according to EUCAST 9.3.1 methodology. Visually-set MICs were compared with spectrophotometrically-obtained MICs (fungal growth reduction >95% compared to control and read at 540 nm); essential (±1 twofold dilution) and categorical agreement were calculated. Errors were classified as very major (isolate classified as resistant by visual MIC and as susceptible by spectrophotometric reading) and major (isolate classified as susceptible by visual MIC and as resistant by spectrophotometric reading).

Results: Overall, essential agreement was 97%, with amphotericin B and posaconazole showing the highest agreement (Table). Categorical agreement was very high (98%) as well, with a total of 1.8% very major errors found in six A. fumigatus sensu stricto isolates that were resistant to either voriconazole and isavuconazole [n=3] or to isavuconazole [n=3], and four cryptic species (N. udagawae [n=2], A. fumigatiaffinis [n=2]). No very major errors were found with amphotericin B or itraconazole. Major errors were scarce and exclusively found with voriconazole and posaconazole against A. fumigatus sensu stricto (<1%; n=5 isolates). All cyp51 gene mutants were correctly classified as resistant. Most of errors occurred in MICs just one two-fold dilution above the breakpoint.

Conclusions: MICs of azoles and amphotericin B against A. fumigatus obtained either by spectrophotometer or visually showed very high agreement. Cyp51A mutants were correctly classified as resistant and most misclassifications occurred in MICs just one two-fold dilution above the breakpoint.

Presenter email address: jguineaortega@yahoo.es


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Full conference title: 

European Congress of Clinical Microbiology and Infectious Diseases 2020
    • ECCMID 30th (2020)