Inhibitor-based methods for the detection of KPC carbapenemase-producing Enterobacteriaceae in clinical practice by using boronic acid compounds

Enterobacteriaceae clinical strains that produce the class A carbapenem-hydrolysing enzyme KPC (Klebsiella pneumoniae carbapenemase) are increasingly reported worldwide, and are already endemic in North and South America, China, Israel and Greece. The accurate detection of KPC enzymes is of utmost importance for containing the global spread of KPC producers. Currently, the detection of putative carbapenemase production is based on an initial phenotypic screen for carbapenem resistance followed by the modified Hodge test (MHT) as a confirmatory test. However, the MHT is often difficult to interpret, is not specific for carbapenemase activity due to KPC and there are reports of false-positive results with CTX-M-positive or AmpC-hyper-producing Enterobacteriaceae. Boronic acid compounds are serine-type beta-lactamase inhibitors that were employed originally for the detection of class C plasmidic AmpCs in Enterobacteriaceae. Recently, they have also been evaluated for the differentiation of KPC-producing Enterobacteriaceae. In that respect, combined-disc tests using carbapenems with and without phenylboronic acid (PBA) have been proposed as the most accurate phenotypic tests for detecting KPC production. When these disc tests are extended to include carbapenem discs with EDTA or both PBA and EDTA on the same plate, the production of metallo-B-lactamase (MBL) or both KPC and MBL, respectively, can also be accurately detected. Phenotypic tests based on the inhibitory activity of boronic acid compounds are very easy to perform and interpret, and may be applied from the first day of isolation of the suspected resistant Enterobacteriaceae. We think that they could effectively replace MHT for the convenient and early detection of KPC carbapenemases in regions where these enzymes are common.