Detection of carbapenemase-producers: Evaluating the performance of the carbapenem inactivation method and Carba NP test versus multiplex PCR

Objectives: With a worrisome surge of carbapenem-resistant bacterial isolates, the diagnostic arsenal has become in dire need of affordable and timely assays to detect the rapidly transmissible carbapenemases. Employing multiplex PCR as a reference method, the purpose of the present study was to compare the performance of the carbapenem inactivation method (CIM) and the Carba NP test in the detection of carbapenemase-producers. Methods: A panel of 203 Gram-negative bacterial isolates screened for carbapenem resistance were subjected to the CIM and Carba NP test. The results were compared with multiplex PCR targeting various carbapenemase genes. Results: According to multiplex PCR, 92 (45.3%) of 203 isolates were found to harbour one or more carbapenemase genes, with blaNDM and blaKPC being the most commonly encountered. The sensitivity and specificity of the CIM were 95.7% and 95.5% respectively, whilst those of the Carba NP test were 75.0% and 99.1%, respectively. Both methods were found to be rapid and reliable in the detection of carbapenemases and showed a high agreement with multiplex PCR. Conclusions: As the list of carbapenemase genes continues to expand, the reliability of PCR has become doubtful; hence, the CIM and Carba NP test could offer promising alternatives, with the CIM being of a lower cost and less labour intensive. (C) 2017 International Society for Chemotherapy of Infection and Cancer. Published by Elsevier Ltd. All rights reserved.