Multiple colony antifungal susceptibility testing detects polyresistance in clinical Candida cultures: a European Confederation of Medical Mycology excellence centers study

Miriam A Knoll; Nina Lackner; Hanno Ulmer; Eldina Samardzic; Joerg Steinmann; Robert Krause; Hedda L Verhasselt; Peter-Michael Rath; Frieder Fuchs; Philipp Koehler; Blandine Denis; Samia Hamane; Alexandre Alanio; Cornelia Lass-Flörl

doi:10.1016/j.cmi.2022.04.014

Multiple colony antifungal susceptibility testing detects polyresistance in clinical Candida cultures: a European Confederation of Medical Mycology excellence centers study

Clin Microbiol Infect. 2022 Sep;28(9):1288.e1-1288.e7. doi: 10.1016/j.cmi.2022.04.014. Epub 2022 May 9.

Authors

Affiliations

¹ Institute of Hygiene and Medical Microbiology, ECMM Excellence Center, Medical University of Innsbruck, Innsbruck, Austria.
² Department of Medical Statistics, Informatics and Health Economics, Medical University of Innsbruck, Innsbruck, Austria.
³ Institute of Clinical Hygiene, Medical Microbiology and Infectiology, Paracelsus Medical University, Klinikum, Nurnberg, Germany; Institute of Medical Microbiology, ECMM Excellence Center, University Hospital Essen, University of Duisburg-Essen, Essen, Germany.
⁴ Biotechmed, Graz, Austria; Division of Infectious Diseases, ECMM Excellence Center, Department of Internal Medicine, Medical University of Graz, Austria.
⁵ Institute of Medical Microbiology, ECMM Excellence Center, University Hospital Essen, University of Duisburg-Essen, Essen, Germany.
⁶ Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, Medical Faculty and University Hospital of Cologne, Cologne, Germany; Department of Microbiology and Hospital Hygiene, Bundeswehr Central Hospital Koblenz, Koblenz, Germany.
⁷ Department I of Internal Medicine, ECMM Excellence Center, Critical Care Medicine, University Hospital of Cologne, Cologne, Germany; Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Cologne, Germany.
⁸ Infectious Diseases Department, ECMM Excellence Center, Hôpital Saint-Louis, APHP, Paris, France.
⁹ Infectious Diseases Department, ECMM Excellence Center, Hôpital Saint-Louis, APHP, Paris, France; Mycology-Parasitology Department, Hôpital Saint-Louis, APHP, Paris, France.
¹⁰ Mycology-Parasitology Department, Hôpital Saint-Louis, APHP, Paris, France; Université de Paris, Molecular Mycology Unit, CNRS UMR2000, National Reference Centre for Invasive Mycoses and Antifungals, Institut Pasteur, Université de Paris, Paris, France.
¹¹ Institute of Hygiene and Medical Microbiology, ECMM Excellence Center, Medical University of Innsbruck, Innsbruck, Austria. Electronic address: cornelia.lass-floerl@i-med.ac.at.

PMID: 35537592
DOI: 10.1016/j.cmi.2022.04.014

Abstract

Objectives: Many factors influence the outcome of in vitro antifungal susceptibility testing (AFST), including endpoint definition, inoculum sizes, time and temperature of incubation, and growth medium used. This European Confederation of Medical Mycology (ECMM) Excellence center driven study investigated multiple colony testing (MCT) of five separate colonies to investigate the prevalence of polyresistance (PR), defined as heterogeneous MICs from a same-species Candida culture irrespective of the underlying resistance mechanism.

Methods: Candida spp. MCT for fluconazole and anidulafungin was performed by Etest prospectively comprising 405 clinical samples. MCT results were compared to the real-life routine MIC data and PR was assessed. Candida colonies displaying strong PR were selected for genotyping using multilocus sequence typing and random amplified polymorphic DNA assays for C. lusitaniae.

Results: Candida PR was observed in 33 of 405 samples (8.1%), with higher rates for non-albicans species (26/186, 14%) than for C. albicans (7/219, 3.2%), and for fluconazole than for anidulafungin. MCT detected acquired resistance more often than routine AFST (18/405, 4.5%) and 9 of the 161 investigated blood cultures showed PR (5.6%). Multilocus sequence typing and random amplified polymorphic DNA did not reveal a uniform genetic correlate in strains studied.

Conclusions: This study shows that Candida single MIC-values obtained in routine diagnostics may be incidental, as they fail to detect PR and resistant subpopulations reliably. The reasons for PR seem to be manifold and should be regarded as a phenotypical expression of genomic variability irrespective of the underlying resistance mechanism, which may help to interpret ambiguous and non-reproducible AFST results.

Keywords: Antifungal resistance; Antifungal susceptibility testing; Candida; Multiple colony testing; Polyresistance.

MeSH terms

Anidulafungin
Antifungal Agents / pharmacology
Candida albicans
Candida* / genetics
Drug Resistance, Fungal
Fluconazole* / pharmacology
Humans
Microbial Sensitivity Tests
Mycology

Substances

Antifungal Agents
Fluconazole
Anidulafungin