Evaluation of phenotypic and genotypic approaches for the detection of class A and class B carbapenemases in Enterobacteriaceae.

The spread of carbapenemases in Enterobacteriaceae is among the most important issues in the antimicrobial resistance. The rapid and recent diffusion of class A and B carbapenemases determined the need of specific diagnostic tests able to detect with high sensitivity this type of resistance and to discriminate between the different enzymes. The aim of this study was to test two carbapenemase detection assays, the Rosco Synergic and the Hyplex polymerase chain reaction-enzyme-linked immunosorbent assays for screening carbapenemase-producing Enterobacteriaceae. The phenotypic and genotypic tests were evaluated among 108 clinical isolates, including Klebsiella pneumoniae carbapenemase (KPC) (n=50) and metallo-β-lactamase- (MBL) (n=20), and AmpC- (n=10) producing Enterobacteriaceae. The commercial phenotypic assay showed a high sensitivity performance detecting all KPC and MBL producers, including New Delhi MBL 1 (NDM-1) strains. In addition, the Rosco Synergic assay was able to distinguish specifically between the different mechanisms that confer resistance to carbapenems in Enterobacteriaceae. We also demonstrated that the genotypic test was able to detect all the class A and B carbapenemases showing high sensitivity (100%) and specificity (98%) in a fast and reliable time. Based on these results, both the commercial phenotypic and the genotypic assays could be helpful as confirmatory and discriminatory tests for the detection of class A and class B carbapenemases.