Rapid detection of carbapenemase-producing Klebsiella pneumoniae: A comparative study of CIM and MHT

Objective: This study aimed to compare the performance of the carbapenem inactivation method (CIM) and the modified hodge test (MHT) to screen carbapenemase activity in Klebsiella pneumoniae isolates with genotypically confirmed results. Materials and Methods: A total of 114 carbapenem-resistant K. pneumoniae clinical isolates were collected from hospitalized patients. Two methods, the MHT and CIM, were used to investigate carbapenemase production. The CIM test was evaluated at the 6th hour for the preliminary decision and the 24th hour for the final decision. MHT was evaluated at the 24th hour. A polymerase chain reaction (PCR) was performed to detect carbapenemase-encoding genes (blaKPC, blaNDM, blaIMP, blaVIM, and blaOXA-48). Results: Of these isolates in which a carbapenemase enzyme was detected by PCR, blaOXA-48 was found in 87.7%, blaKPC in 6.1%, blaNDM in 6.1%, blaIMP in 0.8%, and blaVIM in 0.8%. The most common carbapenemase gene detected was OXA-48. Of the 114 isolates with a genotypically detected carbapenemase enzyme, 98 and 109 were positive by CIM at the 6th and 24th hour, respectively, and 88 by MHT. The isolates producing both blaOXA-48 and blaNDM and blaIMP and blaVIM were detected as positive by both phenotypic tests. The sensitivity of CIM at the 6th and 24th hour and MHT was found to be 85.9%, 95.6%, and 77.1%, respectively. Conclusion: These findings indicate that CIM can be an effective method for accurately and rapidly detecting carbapenemase activity in K. pneumoniae infections, particularly in clinical microbiological laboratories with limited resources. To verify the negative tests, molecular methods are recommended to predict OXA-48 activity particularly..