Ann Lab Med 2020; 40(4): 306-311  https://doi.org/10.3343/alm.2020.40.4.306
Determination of Colistin Resistance by Simple Disk Diffusion Test Using Modified Mueller-Hinton Agar
Jean Damascene Uwizeyimana, M.D.1,2,3, Daewon Kim, M.D.1, Hyunsook Lee, M.Sc.1,4, Jung-Hyun Byun, M.D.1,5, and Dongeun Yong, M.D., Ph.D.1,4
1Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul, Korea; 2Department of Global Health Security, Yonsei University Graduate School of Public Health, Seoul, Korea; 3Department of Emergency Care, Ruli Hospital, Gakenye, Rwanda; 4Brain Korea 21 plus Program for Medical Science, Yonsei University College of Medicine, Seoul, Korea; 5Department of Laboratory Medicine, Gyeongsang National University Hospital, Gyeongsang National University College of Medicine, Jinju, Korea
Corresponding author: Jung-Hyun Byun, M.D.
Department of Laboratory Medicine, Gyeongsang National University Hospital, Gyeongsang National University College of Medicine, Jinju 52727, Korea
Tel: +82-55-750-8423 Fax: +82-55-762-2696. E-mail: microbyun@gmail.com

Dongeun Yong, M.D., Ph.D.
Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
Tel: +82-2-2228-2454 Fax: +82-2-364-1583. E-mail: deyong@yuhs.acdeyong@yuhs.ac
Received: June 3, 2019; Revised: October 8, 2019; Accepted: February 7, 2020; Published online: July 1, 2020.
© Korean Society for Laboratory Medicine. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background: Colistin has become a last-resort antibiotic for the management of multidrug-resistant gram-negative bacteria. The disk diffusion test is cheap and easy to perform but may be unreliable for colistin susceptibility testing due to poor diffusion of the large colistin molecule. An improved agar diffusion test would increase the reliability of colistin susceptibility testing. This study aimed to modify Muller-Hinton agar (MHA) to improve colistin diffusion in agar.
Methods: MHA was modified by reducing the agar concentration from 100% to 30% and supplementing with protamine. We tested 60 gram-negative clinical isolates of Pseudomonas aeruginosa (N=27) and Acinetobacter calcoaceticus-baumannii complex (N=33). Disk diffusion test results were interpreted based on minimum inhibitory concentrations determined by broth microdilution.
Results: The modified MHA yielded the best performance metrics, including 94.7% sensitivity, 100% specificity, and an area under the curve of 0.995 (95% confidence interval, 0.982–1.000), P<0.001, at a cut-off point of 13 mm.
Conclusions: A reduction of the agar concentration from 100% to 30% and the addition of protamine improved colistin diffusion in agar and allowed routine colistin susceptibility testing in a clinical microbiology laboratory, but should be handled with caution.
Keywords: Colistin, Disk diffusion, Colistin susceptibility testing, Muller-Hinton agar, Protamine



This Article

e-submission

Archives

Indexed/Covered by