Carbapenemase-Producing Carbapenem-Resistant Enterobacteriaceae from Bangkok, Thailand, and Their Detection by the Carba NP and Modified Carbapenem Inactivation Method Tests

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 bla(KPC), bla(NDM), bla(VIM), bla(IMP), and bla(OXA-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 bla(NDM) (bla(NDM-1), (-4), (-5), (-9)), bla(OXA) (bla(OXA-48), (-181), (-232)), and bla(IMP-14), were found. Of these, 223 (77.70%) carried at least one of the carbapenemase genes. The bla(NDM) was detected in 160/223 (71.75%) isolates, of which 153/160 (95.63%) were the bla(NDM-1). Three types of the bla(OXA-48-like) group, bla(OXA-48), bla(OXA-181), and bla(OXA-232), were found, 91/104 (87.5%) harbored the bla(OXA-232). In addition, 25.11% (56/223) of the carbapenemase-producing isolates harbored a combination of bla(NDM) and bla(OXA-48-like). Phenotypic detection methods, mCIM and Carba NP, showed 100% sensitivity and specificity to bla(NDM), bla(IMP-14), and bla(OXA-48), while the mCIM was positive in all bla(OXA-181) and bla(OXA-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 bla(NDM-1) and bla(OXA-232) were predominant.