Carbapenem-resistant Enterobacteriaceae (CRE) represent a clinically important group of organisms with limited treatment options that contribute to infections with high mortality rates. In this study, we utilized several different methods to determine resistance mechanisms in CRE to elucidate the mode of resistance and compare results among these methods. Forty-one unique ertapenem-resistant patient isolates obtained over a 4-year period were tested utilizing 4 phenotypic testing methods: Modified Hodge test (MHT), Modified Carbapenem Inactivation Method (mCIM), KPC/Metallo-β-Lactamase (MBL) Confirm KitTM, and Neo-Rapid CARB KitTM. Genotypic testing via Xpert Carba-R (Cepheid, Sunnyvale, USA) was considered the benchmark to which phenotypic testing was compared. Presence of a carbapenemase was detected by all phenotypic tests in 48.7% (n = 20/41) of isolates. Genotypic testing indicated that the majority of isolates produced Klebsiella pneumoniae carbapenemase (KPC) (n = 26/41, 63.4%); no other carbapenemases were identified. These results may aid in informing optimal empiric antimicrobial therapy within the institution when carbapenem resistance is suspected or proven.
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