Carbapenem inactivation, an alternative method to detect carbapenemase type KPC in Enterobacteriacea

Objective: To compare the carbapenem inactivation method (CIM *) with the Modified Hodge Test (MHT), the acid 3-aminophenylboronic test(APB) and the polymerase chain reaction (PCR) detection of the blaKPC gene for the identification of KPC carbapenemase producing Enterobacteriaceae (ECP). Materials and Methods: We selected 88 susceptible and 91 carbapenems resistant clinical isolates of Klebsiella pneumoniae, Klebsiella oxytoca, Escherichia coli, Serratia marcescens and Citrobacter freundii. We performed APB and CIM* according to previously published methods and the MHT according to CLSI 100S Edition 26-2016. The blaKPC gene was identified by PCR multiplex. Results: The CIM* had a sensitivity and specificity close to 100[%] and a kappa score of 1 compared with gold standard PCR. The absence of zone diameter was observed in all isolated KPC producers, unlike in isolates susceptible to carbapenems, where a zone diameter > 19mm was observed. Three percent of false positive and five percent of false negative was observed in THM and ABP respectively. Discussion and conclusions: The CIM* and the PCR were better than MHT and ABP at identifying carbapenemases in ECP. We recommend the routine use of the CIM* within the algorithm for ECP infection control.