Application of Modified Carbapenem Inactivation Method and Its Derivative Tests for the Detection of Carbapenemase-Producing Aeromonas

Yunying Wang,1 Hui Liu,2 Lijun Zhang,1 Bin Sun1 1Department of Laboratory Medicine, The Second Affiliated Hospital of Chongqing Medical University, Chongqing, People’s Republic of China; 2Department of Blood Transfusion, The First Affiliated Hospital of Chongqing Medical University, Chongqing, People’s Republic of ChinaCorrespondence: Bin SunDepartment of Laboratory Medicine, The Second Affiliated Hospital of Chongqing Medical University, No. 74 Linjiang Road, Yuzhong District, Chongqing, People’s Republic of ChinaTel +86 23-62887812Fax +86 23-63703244Email sunbin@cqmu.edu.cnPurpose: Infection and transmission of carbapenem-resistant Aeromonas is a serious threat to public health. Rapid and accurate detection carbapenem-resistant of these organisms is essential for reasonable treatment and infection control. This study aimed to find a simple and effective method to detect carbapenem-resistant phenotype in Aeromonas.Methods: A total of 131 clinical preserved Aeromonas strains were used in this study. The carbapenemase genes were detected by PCR. Modified carbapenem inactivation method (mCIM) in conjunction with EDTA-modified carbapenem inactivation method (eCIM) and simplified carbapenem inactivation method (sCIM) were performed to detect carbapenemases. We also designed a simple method, carbapenem inactivation method using supernatant (CIM-s), to detect the carbapenemase activity in the medium.Results: Of the 131 Aeromonas strains, 79 contained carbapenemase genes, including 68 blaCphA, 6 blaKPC-2, 2 blaNDM-1 and 3 blaKPC-2+CphA. However, routine antibiotic susceptibility testing could not completely identify carbapenemase-producing Aeromonas. In phenotypic assays, the sensitivity and specificity of mCIM were 100%. The combined mCIM and eCIM could distinguish serine carbapenemase and metallo-β-carbapenemases except co-producing organisms. The sensitivity and specificity of sCIM were 92.4% and 100%, respectively, which could not detect CphA totally. CIM-s results indicate that these carbapenemases could secrete into the medium to perform their hydrolytic activities and had a sensitivity and specificity of 97.5% and 100%, respectively.Conclusion: The combination of mCIM and eCIM can effectively detect and distinguish different types of carbapenemase in Aeromonas, and could be used as an important supplement approach to the antibiotic susceptibility testing.Keywords: Aeromonas, modified carbapenem inactivation method, carbapenemase, multidrug resistant, phenotypic detection