Aim: The purpose of the study was to determine the epidemiology of carbapenemase genes among carbapenem-resistant Enterobacteriaceae and evaluate the Carba NP and modified carbapenem inactivation method (mCIM) tests in their detection.
Materials and methods: A total of 287 nonduplicated Enterobacteriaceae isolates, which were at least resistant to one of the carbapenems, were identified and detected for carbapenemase genes by multiplex PCR covering blaKPC, blaNDM, blaVIM, blaIMP, and blaOXA-48-like. All positive genes were then sequenced. These isolates were phenotypically tested for the production of carbapenemases by mCIM and Carba NP tests to evaluate the efficacy of these methods.
Results: Seven species of carbapenem-resistant isolates mainly Klebsiella pneumoniae, Escherichia coli, and Enterobacter cloacae were detected. Of these isolates, three families of carbapenemase genes, including blaNDM (blaNDM-1, -4, -5, -9), blaOXA (blaOXA-48, -181, -232), and blaIMP-14, were found. Of these, 223 (77.70%) carried at least one of the carbapenemase genes. The blaNDM was detected in 160/223 (71.75%) isolates, of which 153/160 (95.63%) were the blaNDM-1. Three types of the blaOXA-48-like group, blaOXA-48, blaOXA-181, and blaOXA-232, were found, 91/104 (87.5%) harbored the blaOXA-232. In addition, 25.11% (56/223) of the carbapenemase-producing isolates harbored a combination of blaNDM and blaOXA-48-like. Phenotypic detection methods, mCIM and Carba NP, showed 100% sensitivity and specificity to blaNDM, blaIMP-14, and blaOXA-48, while the mCIM was positive in all blaOXA-181 and blaOXA-232 isolates, only 12.5% (1/8) and 28.95% (11/38), respectively, were detected by the Carba NP test.
Conclusions: This study revealed a unique prevalence of carbapenemase genes in Bangkok, Thailand, as well as demonstrated the efficacy and limitation of phenotypic detection methods of carbapenemase in the area where blaNDM-1 and blaOXA-232 were predominant.
Keywords: CRE; Carba NP test; OXA-181; OXA-232; mCIM.