Development and evaluation of the method for detecting metallo-carbapenemases among carbapenemase-producing Enterobacteriaceae

A simple EDTA synergistic carbapenem inactivation method (esCIM) based on the simplified carbapenem inactivation method (sCIM) and EDTA synergistic carbapenem inactivation test (eCIM) detected the levels of metallo-beta-lactamases (MBLs) carbapenemase. The esCIM method uses EDTA-impregnated antibiotic disk to detect carbapenemase-producing Enterobacteriaceae (CPE) directly instead of inculating the disk in the trypticase soy broth (TSB). To determine the sensitivity and specificity of esCIM, 167 carbapenemase-resistant Enterobacteriaceae (CRE) isolates were collected, of which, 161 were CPE strains confirmed by PCR. The carbapenemase genes included blaKPC (50.9%), blaNDM (36.6%), blaIMP (6.8%), blaVIM (3.1%), and blaOXA-181 (0.6%). Three isolates carried two different types of genes (blaKPC and blaNDM), and the remaining six CRE strains lacked the carbapenemase genes. The phenotypic evaluations were performed using both esCIM and eCIM. The esCIM performs better than eCIM in the detection of blaNDM and blaIMP, and the positive rate of eCIM was 83% and 55% for blaNDM and blaIMP, respectively. However, in the case of esCIM, the rate increased to 97% and 73%, respectively. For all MBLs, the sensitivity of esCIM and eCIM observed was 91% and 76%, respectively, while the specificity of the two methods was 100%. Taken together, esCIM could be performed easily and interpreted quickly.