Phenotypic and genotypic investigation of carbapenemases in carbapenem-resistant Klebsiella pneumoniae isolates.

Carbapenem resistance in Klebsiella pneumoniae is primarily mediated by carbapenemase production. This study aimed to identify carbapenemase genes in carbapenem-resistant K. pneumoniae isolates using multiplex polymerase chain reaction (PCR) and to evaluate the performance of the combination disk assay (CDA) as a phenotypic detection method. A total of 123 carbapenem-resistant K. pneumoniae isolates were analyzed. Colistin and meropenem susceptibility were deter - mined by broth microdilution, while ceftazidime-avibactam susceptibility was assessed using disk diffusion. Five common carbapenemase genes ( blaOXA-48, blaNDM, blaKPC, blaIMP, blaVIM) were detected by multiplex PCR. CDA was per - formed using meropenem and temocillin disks in combination with specific inhibitors (EDTA, boronic acid, cloxacillin). Colistin (59.3%) and ceftazidime-avibactam (58.5%) showed the highest susceptibility rates. PCR identified blaOXA-48 in 53.6%, blaKPC in 45.5%, and blaNDM in 32.5% of isolates. CDA detected MBL, KPC, and OXA-48 enzymes in 44.7%, 44.7%, and 10.6% of isolates, respectively, and failed to detect OXA-48 in the presence of NDM. Compared with PCR, CDA showed excellent agreement for KPC detection (sensitivity 100%, specificity 100%; κ = 0.984), moderate agreement for MBL (sensitivity 95%, specificity 76.1%; κ = 0.679), and poor agreement for OXA-48 (sensitivity 19.7%, specificity 100%; κ = 0.185). CDA may be used as an initial phenotypic screening tool for the detection of KPC-producing isolates; however, its limited ability to detect OXA-48 and carbapenemase co-production restricts its reliability for broader clinical interpretation. Therefore, PCR-based