Evaluation of Phenotypic Carbapenemase Production in blaOXA-48 positive K. pneumoniae Isolates by Modified Hodge and Carbapenemase Inactivation Tests

Abstract

Aim:In recent years, increasing colonization rates of K. pneumoniae in patients with immunosuppression, long hospital stay, invasive devices and treated with broad spectrum antibiotics lead to resistant infections. In this investigate, we aimed to investigate carbapenem resistance in multiresistant K. pneumoniae isolates derived from clinical specimens by phenotypic and genotypic methods.Materials and Methods:In July 2014, 51 K. pneumoniae isolates which were derived from clinical specimens were evaluated. Identification and antibiotic susceptibility tests of isolates were studied with automatized system. Verification of carbapenem resistance were studied with with gradient strip tests. Identification of carbapenemase resistant genes were studied with with “in house” PCR. Phenotypic tests including Modified Hodge test (MHT) and Carbapenemase Inactivation Method (CIM) were applied to all isolates. We re-studied all carbapenems for the isolates with incompatible results.Results:Resistance rates of all isolates to imipenem, meropenem and ertapenem were 78.43%, 60.78% and 96.08%, respectively. 42 of 51 isolates were positive with MHT and 43 of 51 isolates were positive with CIM. blaOXA-48 gene was identified in 42 isolates with PCR. nine isolates which were negative for blaOXA-48 and other carbapenemases gene were negative with MHT and eight isolates which were negative for blaOXA-48 gene were negative with CIM.Conclusion:MHT and CIM are fast and easy methods for the identification of carbapenemase presence. CIM is an easy screening test, but one should be cautious for false negative and positive results. We suggest that modification of the test with carbapenem discs should decrease false negative results.

Keywords

• oxa-48
• carbapenem resistance
• modified hodge test
• carbapenem inactivation method
• pcr