Within-a-Day Detection and Rapid Characterization of Carbapenemase by Use of a New Carbapenem Inactivation Method-Based Test, CIMplus

Abstract

The dissemination of carbapenemase-producing Enterobacteriaceae (CPE) is a major threat to public health. Rapid and accurate detection of CPE is essential for initiating appropriate antimicrobial treatment and establishing infection control measures. The carbapenem inactivation method (CIM), which has good sensitivity and specificity but a detection time of 20 h, was recently described. In this study, we evaluated the performances of a new version, the CIMplus test, which allows detection of carbapenemases in 8 h and characterization of carbapenemase classes, according to the Ambler classification, in 20 h. A panel of 110 carbapenem-resistant Enterobacteriaceae strains, including 92 CPE strains (with NDM, VIM, IMP, KPC, GES, OXA-48, and OXA-48-like enzymes), was used to evaluate test performance. Carbapenemase activity was detected at 8 h and 20 h. Characterization of carbapenemase classes, using specific inhibitors, was possible in 20 h. The CIMplus test had sensitivities of 95.7% and 97.8% at 8 h and 20 h, respectively, and a specificity of 94.4%, independent of the culture duration. Using a decision algorithm, this test was successful in identifying the carbapenemase class for 98.9% of tested CPE isolates (87/88 isolates). In total, the characterization was correct for 100%, 96.9%, and 100% of Ambler class A, B, and D isolates, respectively. Therefore, this test allows detection of carbapenemase activity in 8 h and characterization of carbapenemase classes, according to the Ambler classification, in 20 h. The CIMplus test represents a simple, affordable, easy-to-read, and accurate tool that can be used without any specific equipment.

Keywords: EDTA; Enterobacteriaceae; NDM; OXA-48; carbapenemase; carbapenemase inactivation method; mCIM; phenotypic characterization; phenotypic detection; phenylboronic acid.

FIG 1

Strategy to identify the type of carbapenemase by using meropenem disks (10 μg) with or without a specific carbapenemase inhibitor (PBA for class A enzymes and EDTA for class B enzymes).

FIG 2

Examples of results for different carbapenemase classes identified with the CIMplus test at 8-h readings. (A) RD30 (KPC). (B) RD7 (NDM). (C) RD4 (OXA-48). (D) SL1 (absence of carbapenemase). The culture of E. coli ATCC 25922 grows to contact the meropenem disks with the CPE isolates (A, B, and C), whereas an inhibition zone diameter is detected with the carbapenemase nonproducer (D).