Evaluation of CHROMagar™mSuperCARBA™ as a Phenotypic Test for Detection of Carbapenemase Producing Organisms

Abstract

Introduction: Carbapenem resistance among Enterobacteriaceae continues to escalate. Carbapenemase encoding genes borne on plasmids leads to wide-spread transmission among Enterobacteriaceae. The accurate and rapid detection of Carbapenemase producing-Carbapenem resistant Enterobacteriaceae (CP-CRE) is imperative for patient management as well as for hospital infection control measures. We therefore evaluated the CHROMagar™mSuperCARBA™ (CMSCs) a phenotypic screening test for detection of CP-CRE. Aim: To evaluate the performance of CMSCs as a phenotypic test for detection of carbapenemase producing organisms. Materials and Methods: A total of 150 consecutive Carbapenem resistant Enterobacteriaceae (CRE) (E. coli n=81 and Klebsiella spp. n=69), isolated from consecutive hospitalised patients with significant bacteriuria, were subjected to CRE Multiplex PCR for the detection of blaKPC, blaNDM, blaVIM, blaOXA-48 like and blaIMP genes. Phenotypic detection of carbapenemase production was evaluated by the chromogenic medium CMSC, CarbaNP and Modified Hodge Test (MHT). Results: The multiplex PCR detected carbapenemase encoding gene(s) in 108 isolates. The sensitivity of CMSC, CarbaNP test and MHT in detecting isolates carrying blaNDM and blaOXA48-like genes was 94.4%, 67.6%, 56.3% and 96%, 40.8%, 38.8% respectively. While overall sensitivity of CMSC, CarbaNP test and MHT for detection of CP-CRE was 85.3%, 46.6% and 40% respectively; with a negative likelihood ratio of 0.18, 0.55 and 0.64 respectively. Conclusion: CMSC emerged as the most sensitive test for detection of isolates carrying blaNDM and blaOXA48-like genes, with an excellent negative likelihood ratio. In addition, it was found to be inexpensive and has the fastest turnaround time. It is a promising phenotypic test especially in geographic regions with wide spread resistance due to blaNDM and blaOXA48-like CP-CRE.

Keywords

• carbapenem resistant enterobacteriaceae
• chromogenic medium
• oxa-48-like