The optimized carbapenem inactivation method for objective and accurate detection of carbapenemase-producing Acinetobacter baumannii

Sirui Zhang; Peng Mi; Jingdan Wang; Pu Li; Kai Luo; Shuyan Liu; Mona Mohamed Al-Shamiri; Jin'e Lei; Simin Lai; Bei Han; Yanjiong Chen; Lei Han; Shaoshan Han

doi:10.3389/fmicb.2023.1185450

The optimized carbapenem inactivation method for objective and accurate detection of carbapenemase-producing Acinetobacter baumannii

Front Microbiol. 2023 Jul 13:14:1185450. doi: 10.3389/fmicb.2023.1185450. eCollection 2023.

Authors

Sirui Zhang¹, Peng Mi^{1

2}, Jingdan Wang³, Pu Li³, Kai Luo¹, Shuyan Liu¹, Mona Mohamed Al-Shamiri¹, Jin'e Lei⁴, Simin Lai¹, Bei Han³, Yanjiong Chen¹, Lei Han¹, Shaoshan Han⁵

Affiliations

¹ Department of Microbiology and Immunology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science Center, Xi'an, China.
² Department of Laboratory Medicine, Shaanxi Provincial People's Hospital, Xi'an, China.
³ School of Public Health, Xi'an Jiaotong University Health Science Center, Xi'an, China.
⁴ Department of Laboratory Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, China.
⁵ Department of Hepatobiliary Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, China.

Abstract

The modified carbapenem inactivation method (mCIM) recommended by the Clinical and Laboratory Standards Institute is not applicable for detecting carbapenemases in Acinetobacter baumannii. Four currently reported phenotypic detection methods, namely, the modified Hodge test, the mCIM, the adjusted mCIM, and the simplified carbapenem inactivation method (sCIM), did not perform well in our 90 clinical A. baumannii isolates. Thus, the minimal inhibitory concentrations (MICs) of carbapenems and the existence and expression of carbapenemase-encoding genes were detected to explain the results. According to the E-test, which was more accurate than the VITEK 2 system, 80.0 and 41.1% were resistant to imipenem (IPM) and meropenem (MEM), respectively, and 14.4 and 53.3% exhibited intermediate resistance, respectively. Five β-lactamase genes were found, of which bla_OXA-51-like, bla_TEM, and bla_OXA-23-like were detected more frequently in 85 non-susceptible strains. The expression of bla_OXA-23-like was positively correlated with the MIC values of IPM and MEM. Therefore, an improved approach based on the mCIM, designated the optimized CIM (oCIM), was developed in this study to detect carbapenemases more accurately and reproducibly. The condition was improved by evaluating the factors of A. baumannii inoculum, incubation broth volume, and MEM disk incubation time. Obvious high sensitivity (92.94%) and specificity (100.00%) were obtained using the oCIM, which was cost-effective and reproducible in routine laboratory work.

Keywords: Acinetobacter baumannii; carbapenemase; carbapenemases gene expression; minimal inhibitory concentrations; modified carbapenem inactivation method; optimized carbapenem inactivation method.