Phenotypic detection of carbapenemase production in carbapenem-resistant isolates with the rapid carbapenemase detection method (rCDM)

Carbapenem antibiotics are widely used for the treatment of infections caused by multidrug-resistant bacteria. As a result of this, resistance to carbapenems is gradually increasing. Identification of carbapenemase production, one of the reasons for resistance, through molecular methods is expensive and time-consuming. In the present study, it was aimed to investigate the sensitivity of the newly developed rapid carbapenemase detection method (rCDM) as compared to the gold standard molecular method and to evaluate its consistency with another phenotypical method, the modified carbapenem inactivation method (mCIM). In our study, a total of 152 Gram-negative bacteria (Klebsiella pneumoniae, Escherichia coli) isolated from various clinical samples of which 50 were controls were included. Strain identification was done by using VITEK®MS (bioMérieux, Marcy-I'Étoile, France), carbapenem sensitivity was tested by using VITEK®2 (bioMérieux). For carbapenem-resistant isolates, carbapenem resistance genes were detected with multiplex PCR [Carbapenem and Colistin Resistance qPCR kit (Bioeksen, İstanbul, Turkey)] kit by a molecular method. All included isolates were evaluated by the rCDM and mCIM tests in order to detect carbapenemase phenotypically. The molecular method was accepted to be the gold standard and the sensitivity of rCDM was calculated. The McNemar test was applied to analyze the difference between two phenotypic tests (rCDM and mCIM) and Cohen's Kappa analysis was applied to determine consistency. Out of 102 carbapenem-resistant isolates, at least one of the resistance genes in the multiplex PCR panel (blaKPC, blaNDM, blaVIM, blaIMP, blaOXA₋₅₁, blaOXA₂₃/₅₈, blaOXA₋₄₈) was detected in 92 and blaOXA₋₄₈ was the most common (90.2%). The sensitivity of the rapid carbapenemase detection method was found to be 100%. When the results of the two phenotypic methods were compared, no statistically significant difference could be found (PMcNₑₘₐᵣ:1, Kappa coefficient:1.00). The rapid carbapenemase detection method was found to be suitable to use in routine laboratory analysis as its sensitivity was found to be high, exhibited a good performance for detection of frequent carbapenemase types in our country (Turkey), a high consistency with mCIM, and also it is an easily applied and rapid method.