Evaluation of Phenotypic Tests for Carbapenemase Detection in Enterobacteriaceae in Tunisia

Abstract

Introduction: Resistance to carbapenems in Enterobacteriaceae is a challenge for public health. Carbapenemase production is the leading mechanism. This work aims to evaluate four phenotypic methods for carbapenemase detection in comparison with a molecular method. Materials and Methods: Thirty-seven nonrepeating Enterobacteriaceae strains with decreased susceptibility to ertapenem were included. Imipenem MIC, Modified Hodge Test (MHT), Neo-Rapid Carb Kit ® and KPC, MBL, and OXA-48 Confirm Kit ® were performed. Isolates were tested for bla OXA-48 , bla NDM , and bla VIM genes by end-point polymerase chain reaction. The results of the molecular study were used as a reference test to determine the performances of the phenotypic tests. Results: Imipenem resistance does not seem to be a good marker for carbapenemase production with a sensitivity of 54% (95% CI: 38–71). MHT showed 82% sensitivity (95% CI: 65–91). Overall, the enzymatic test showed the best performances for carbapenemase detection with 100% sensitivity (95% CI: 89–100) and the best turnaround time. The characterization of carbapenemases classes by the combined discs test demonstrated 88% overall sensitivity (95% CI: 72–95). Conclusion: The results of this study support the combination of the enzymatic and the combined disc tests for carbapenemase detection in Enterobacteria.