Rapid detection of carbapenemase production in Enterobacteriaceae by different phenotypic methods

Introduction: Carbapenemase producing enterobacteriaceae (CPE) isolates have now emerged worldwide. Resistance to carbapenems is mainly due to production of beta-lactamases inactivating carbapenems (carbapenemases) included in classes A, B, C, or D of the Ambler classification. In Enterobacteriaceae carbapenemase encoding genes are often located on plasmids that contribute to a rapid spread among clinically relevant gram negative bacteria. Rapid and reliable detection of carbapenemase production is needed for therapeutic and control reasons. Aims: To compare the different phenotypic methods of carbapenemase detection namely, the modified paper strip carba NP method, the CLSI Carba NP method, the carbapenem inactivation method, and for rapid detection of CPE. Materials and methods: A total of 200 CPE from urine, pus, and blood cultures sent to the Microbiology Laboratory, R.G. Kar Medical College and Hospital (RGKMCH), were tested for the modified paper strip carba NP method, the CLSI Carba NP method, and the carbapenem inactivation method. Results and analysis: Out of 200 isolates, 108 isolates of Klebsiella spp and 92 isolates of Escherichia coli were compared for carbapenemase production by various phenotypic methods. In total, 100(93%) isolates of Klebsiella spp and 88 (95%) isolates of Escherichia coli showed positive results by paper strip and carba NP methods. A total of 96 (89%) isolates of Klebsiella spp and 84 (91%) isolates of Escherichia coli showed positive results by CLSI carba NP method. A total of 104 (96%) isolates of Klebsiella spp and 92 (100%) isolates of Escherichia coli showed positive results by CIM method. Conclusion: Rapid and accurate detection of carbapenemase producers are important for preventing their spread in health care settings. Although genotypic tests remain the gold standard but cannot practically be conducted because they are highly expensive and results are limited by the targets. The different phenotypic methods used in this study were inexpensive, rapid, highly sensitive, and specific. The modified paper strip Carba NP method in this study is a simple and rapid method compared to those performed by the CLSI method.