Comparison of Carbapenem Inactivation Test and Modified Hodge Test in Carbapenemase-Producing Klebsiella pneumoniae Strains

Objective: Carbapenem-resistant Enterobacteriaceae are reported increasingly everywhere throughout the world. Rapid and simple detection of carbapenemase-producing strains has become imperative because of the use of carbapenems in the treatment of extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae infections. In this study, we aimed to compare the diagnostic value of modified Hodge test and carbapenem inactivation test for Klebsiella pneumoniae isolates producing carbapenemase, verified by molecular method, and to evaluate their use in routine laboratory practice. Methods: 64 K. pneumoniae strains which have shown resistance gene causing carbapenem resistance by the polymerase chain reaction, and 40 ESBL-negative and carbapenem-susceptible K. pneumoniae strains have been included in this study. Meropenem, imipenem and ertapenem were studied separately in modified Hodge test and carbapenem inactivation test was performed for all strains. Carbapenem inactivation test was evaluated at the 6th hour for preliminary decision and at the 24th hour for the final decision. Results: The sensitivity of the modified Hodge test using meropenem, imipenem and ertapenem for detecting presence of carbapenemase was 60.9%, 62.5% and 68.8%, respectively. In the carbapenem inactivation test with meropenem, imipenem and ertapenem, sensitivity to determine carbapenemase production was 32.8%, 75% and 96.9% after 6 hours, and 64.1%, 84.4% and 96.9% after 24 hours, respectively. There were no positive results in modified Hodge and carbapenem inactivation tests with K. pneumoniae strains that were ESBL-negative and carbapenem-susceptible. Conclusions: As a result, molecular tests are essential to detect carbapenem encoding genes. However, we believe that the carbapenemase inactivation test is a better alternative to the modified Hodge test to detect carbapenemase production in laboratories without adequate infrastructure.