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Open AccessArticle

Comprehensive Statistical Evaluation of Etest®, UMIC®, MicroScan and Disc Diffusion versus Standard Broth Microdilution: Workflow for an Accurate Detection of Colistin-Resistant and Mcr-Positive E. coli

1
Laboratorio de Referencia de Escherichia coli (LREC), Departamento de Microbioloxía e Parasitoloxía, Facultade de Veterinaria, Universidade de Santiago de Compostela (USC), 27002 Lugo, Spain
2
Instituto de Investigación Sanitaria de Santiago de Compostela (IDIS), 15706 Santiago, Spain
3
Servicio de Microbiología, Hospital Universitario Central de Asturias, 33011 Oviedo, Spain
4
Grupo de Microbiología Traslacional, Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), 33011 Oviedo, Spain
5
Research & Innovation, Artificial Intelligence and Statistical Department, iAST™, 33007 Oviedo, Spain
*
Authors to whom correspondence should be addressed.
These authors contributed equally to this paper.
Antibiotics 2020, 9(12), 861; https://doi.org/10.3390/antibiotics9120861
Received: 24 August 2020 / Revised: 12 November 2020 / Accepted: 1 December 2020 / Published: 3 December 2020
(This article belongs to the Special Issue Colistin Resistance: The Need for a One Health Approach)
Four colistin susceptibility testing methods were compared with the standard broth microdilution (BMD) in a collection of 75 colistin-susceptible and 75 mcr-positive E. coli, including ST131 isolates. Taking BMD as reference, all methods showed similar categorical agreement rates (CA) of circa 90%, and a low number of very major errors (VME) (0% for the MicroScan system and Etest®, 0.7% for UMIC®), except for the disc diffusion assay (breakpoint ≤ 11 mm), which yielded false-susceptible results for 8% of isolates. Of note is the number of mcr-positive isolates (17.3%) categorized as susceptible (≤2 mg/L) by the BMD method, but as resistant by the MicroScan system. ST131 mcr-positive E. coli were identified as colistin-resistant by all MIC-based methods. Our results show that applying the current clinical cut-off (>2 mg/L), many mcr-positive E. coli remain undetected, while applying a threshold of >1 mg/L the sensitivity of detection increases significantly without loss of specificity. We propose two possible workflows, both starting with the MicroScan system, since it is automated and, importantly, it categorized all mcr-positive isolates as colistin-resistant. MicroScan should be followed by either BMD or MIC-based commercial methods for colistin resistance detection; or, alternatively, MicroScan, followed by PCR for the mcr screening. View Full-Text
Keywords: E. coli; mcr; colistin; ST131; AST; MicroScan; BMD E. coli; mcr; colistin; ST131; AST; MicroScan; BMD
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MDPI and ACS Style

García-Meniño, I.; Lumbreras, P.; Valledor, P.; Díaz-Jiménez, D.; Lestón, L.; Fernández, J.; Mora, A. Comprehensive Statistical Evaluation of Etest®, UMIC®, MicroScan and Disc Diffusion versus Standard Broth Microdilution: Workflow for an Accurate Detection of Colistin-Resistant and Mcr-Positive E. coli. Antibiotics 2020, 9, 861. https://doi.org/10.3390/antibiotics9120861

AMA Style

García-Meniño I, Lumbreras P, Valledor P, Díaz-Jiménez D, Lestón L, Fernández J, Mora A. Comprehensive Statistical Evaluation of Etest®, UMIC®, MicroScan and Disc Diffusion versus Standard Broth Microdilution: Workflow for an Accurate Detection of Colistin-Resistant and Mcr-Positive E. coli. Antibiotics. 2020; 9(12):861. https://doi.org/10.3390/antibiotics9120861

Chicago/Turabian Style

García-Meniño, Isidro; Lumbreras, Pilar; Valledor, Pablo; Díaz-Jiménez, Dafne; Lestón, Luz; Fernández, Javier; Mora, Azucena. 2020. "Comprehensive Statistical Evaluation of Etest®, UMIC®, MicroScan and Disc Diffusion versus Standard Broth Microdilution: Workflow for an Accurate Detection of Colistin-Resistant and Mcr-Positive E. coli" Antibiotics 9, no. 12: 861. https://doi.org/10.3390/antibiotics9120861

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