Assessment of Phenotypic Testing by mCIM with eCIM for Determination of the type of Carbapenemase Produced by Carbapenem-resistant Enterobacterales

Abstract

Background: Carbapenemase-producing Enterobacterales are increasingly spreading in healthcare facilities. Identifying the type of carbapenemase can help epidemiologic surveillance and proper selection of antimicrobials. Objective: This study assessed the sensitivity and specificity of carbapenem inactivation method (mCIM with eCIM) for identification of carbapenemase-production. Methodology: The study involved 150 isolates of Enterobacterales. Carbapenem-resistant isolates by Kirby Bauer method were further tested for carbapenemase production phenotypically by mCIM with eCIM, and genotypically by multiplex PCR using specific primers for blaKPC, blaOXA-48, blaNDM-1, blaVIM, and blaIMP. Results: Resistance to carbapenem was observed in 53/150 isolates. Phenotypically, 28/53 isolates produced metallo-β-lactamase, 16/53 produced serine carbapenemase, 5/53 isolates gave inconclusive results, and 4/53 were negative by mCIM with eCIM test. Genotypically, 30 isolates carried blaNDM-1, and 41 isolates carried blaOXA-48. Both genes co-existed in 18 Metallo-β-lactamase producers. The 9 isolates with negative or inconclusive results carried carbapenemase-encoding genes. For mCIM with eCIM test the sensitivity and specificity of detecting Metallo-β-lactamase production were higher (87% and 91%) than for serine carbapenemase detection (34% and 83%), respectively. Conclusion: It was concluded that the mCIM with eCIM test does not always lead to true conclusions about the existence and the type of carbapenemase produced by Enterobacterales.