Experience with a Commercial Assay for Detecting Different Carbapenemases in Enterobacteriaceae

Metallo- lactamases and serine carbapenemases in Enterobacteriaceae are rapidly threatening the utility of carbapenems. This has led to the need for specific diagnostic tests to detect these enzymes with high sensitivity and to discriminate between them. Reliable detection of carbapenemases is necessary to implement contact precautions and for outbreak detection. Our aim was to detect Class A Klebsiella pneumoniae carbapenemase (KPC) and similar serine carbapenemases, Class B metallo-beta-lactamases (MBL), and AmpC-type beta-lactamases in carbapenem-resistant Enterobacteriaceae isolates in our teaching hospital, using the proprietary KPC + MBL Detection Kit from Rosco Diagnostica, Denmark. Fifty meropenem-resistant strains isolated at Himalayan Institute of Medical Sciences, Dehradun between November 2013 and June 2014, were analysed with the Rosco KPC + MBL Kit comprising of four disks: meropenem 10 µg (to confirm resistance), meropenem + phenylboronic acid (inhibitor of KPC-type carbapenemases and AmpC-type beta-lactamases), meropenem + dipicolinic acid (inhibitor of MBLs), and meropenem + cloxacillin (inhibitor of AmpC-type betalactamases). The dominant species were Klebsiella pneumoniae with 22 (44%), Escherichia coli with 10 (20%) and Enterobacter cloacae with seven (14%) isolates. The remaining isolates included Enterobacter aerogenes, Citrobacter freundii, Citrobacter koseri, Serratia marcescens, Proteus vulgaris and Proteus mirabilis. Thirty-five (70%) isolates produced MBL, while two (4%) produced both KPC and MBL carbapenemases. The remaining isolates (26%) produced neither KPC-type serine carbapenemases nor metallo-beta-lactamases. Around a quarter of carbapenem-resistant Enterobacteriaceae isolates tested in our hospital did not produce Class A or B carbapenemases or AmpC-type beta-lactamases and are presumed to have been carbapenem resistant with the help of Class D (OXAtype) carbapenemases, efflux pumps, porin loss or a combination of any of these factors. K e y w o r d s Carbapenem resistance, Enterobacteriaceae,