Table_2_The optimized carbapenem inactivation method for objective and accurate detection of carbapenemase-producing Acinetobacter baumannii.XLSX

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 blaOXA-51-like, blaTEM, and blaOXA-23-like were detected more frequently in 85 non-susceptible strains. The expression of blaOXA-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.

临床与实验室标准化协会（Clinical and Laboratory Standards Institute）推荐的改良碳青霉烯灭活试验（modified carbapenem inactivation method, mCIM）并不适用于检测鲍曼不动杆菌（Acinetobacter baumannii）中的碳青霉烯酶。目前已报道的4种表型检测方法，即改良霍奇试验、mCIM、调整型mCIM以及简化碳青霉烯灭活试验（simplified carbapenem inactivation method, sCIM），在本研究的90株临床分离鲍曼不动杆菌中检测效果欠佳。为此，本研究通过检测碳青霉烯类抗生素的最低抑菌浓度（minimal inhibitory concentrations, MICs）以及碳青霉烯酶编码基因的存在与表达情况来阐释上述结果。相较于维特克2系统（VITEK 2），E试验法（E-test）更为准确，结果显示分别有80.0%和41.1%的菌株对亚胺培南（imipenem, IPM）和美罗培南（meropenem, MEM）耐药，另有14.4%和53.3%的菌株分别呈现中介耐药。本研究共检出5种β-内酰胺酶基因，其中blaOXA-51样基因、blaTEM基因以及blaOXA-23样基因在85株非敏感菌株中检出率更高。blaOXA-23样基因的表达水平与亚胺培南、美罗培南的MIC值呈正相关。据此，本研究开发了一种基于mCIM的改良方法，命名为优化型碳青霉烯灭活试验（optimized CIM, oCIM），以更准确且可重复地检测碳青霉烯酶。该方法通过优化鲍曼不动杆菌接种量、孵育液体积及美罗培南纸片孵育时间等关键参数完成条件改进。使用oCIM检测可获得显著优异的灵敏度（92.94%）与特异性（100.00%），且成本低廉、重复性良好，适用于常规实验室工作。