Ann Lab Med 2020; 40(1): 21-26  https://doi.org/10.3343/alm.2020.40.1.21
Adjustment of Modified Carbapenem Inactivation Method Conditions for Rapid Detection of Carbapenemase-Producing Acinetobacter baumannii
Thao Nguyen Vu, B.Sc.1,2, Jung-Hyun Byun, M.D.1,3, Roshan D’Souza, Ph.D.1,4, Naina Adren Pinto, Ph.D.1,2, Le Phuong Nguyen, M.D.1,2, Dongeun Yong, M.D.1, and Yunsop Chong, M.D.1
1Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul, Korea; 2Brain Korea 21 PLUS Project for Medical Science, Yonsei University, Seoul, Korea; 3Department of Laboratory Medicine, Gyeongsang National University College of Medicine, Gyeongsang National University Hospital, Jinju, Korea; 4J. Craig Venter Institute, Rockville, Maryland, USA
Corresponding author: Jung-Hyun Byun, M.D.
Department of Laboratory Medicine, Gyeongsang National University College of Medicine, Gyeongsang National University Hospital, 79 Gangnam-ro, Jinju 52727, Korea
Tel: +82-55-750-8423 Fax: +82-55-762-2696 E-mails: microbyun@gmail.com; jhbyun@gnuh.co.kr
Received: March 15, 2019; Revised: May 10, 2019; Accepted: July 30, 2019; Published online: January 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: The existing modified carbapenem inactivation methods (mCIMs) recommended by the CLSI for detecting carbapenemase production have not been applicable for Acinetobacter baumannii. We evaluated the influence of matrices used in mCIMs and CIMTris on the stability of the disks for detecting carbapenemase producers and suggested optimal mCIM conditions for detecting carbapenemase-producing A. baumannii.
Methods: Seventy-three A. baumannii isolates characterized for antimicrobial susceptibility and carbapenemase encoding genes were tested for carbapenemase production using mCIM and CIMTris. The influence of the matrices (Tryptic soy broth [TSB] and Tris-HCl) used in these methods on the stability of the meropenem (MEM) disk was also evaluated. The mCIM conditions were adjusted to enhance screening sensitivity and specificity for detecting carbapenemase-producing A. baumannii.
Results: The matrices had an impact on the stability of the MEM disk after the incubation period (two or four hrs). TSB nutrient broth is an appropriate matrix for mCIM compared with Tris-HCl pH 7.6, which leads to the loss of MEM activity in CIMTris. The sensitivity and the specificity of the optimal mCIM were both 100%.
Conclusions: We established optimal mCIM conditions for simple, accurate, and reproducible detection of carbapenemase-producing A. baumannii.
Keywords: Carbapenemase, Acinetobacter baumannii, Modified carbapenem inactivation method, CIMTris



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