Investigation of carbapenem resistance in carbapenem-resistant klebsiella pneumoniae strains by phenotypic and genotypic methods

Background: The aim of this study is to test the presence of carbapenemase in carbapenem-resistant Klebsiella pneumoniae strains isolated from clinical specimens by phenotypic and genotypic methods, to determine the distribution of carbapenemase enzyme types and to determine the correlation between test methods. Materials and Methods: 100 K. pneumoniae strains that were resistant to at least one of the carbapenem group antibiotics and isolated from clinical samples sent to Hitit University Çorum Erol Olçok Training and Research Hospital Microbiology Laboratory between March 2021 and March 2022 were included in the study. Identification and antibiogram of bacteria were performed with the automated system VITEK 2 Compact (bioMérieux, France). Combination disc test was used as a phenotypic method to determine carbapenemase resistance. As a genotypic method, two different multiplex polymerase chain reactions targeting the most common carbapenemase resistance genes, blaKPC, blaNDM, blaVIM, blaIMP and blaOXA-48, were applied. Results: It was determined that all samples produced carbapenemase by the combination disc test, and OXA-48-like positivity was found in 87 (87%) isolates and MBL positivity was found in 13 (13%) isolates. Polymerase chain reaction was positive in 91 isolates and 76 (76%) isolates were OXA-48, 13 (13%) isolates were NDM, 2 (2%) isolates were OXA-48 + NDM. In 9 (9%) samples, the investigated resistance genes were not found. KPC, VIM, and IMP were not observed in any of the isolates. The agreement between the two tests was 89%. The sensitivity of the combination disc test for detecting the presence of carbapenemase was found to be 100%, and the positive predictive value was 91%. The sensitivity of the combination disc test for isolates with only have OXA48 was found to be 100%, specificity 54.1%, positive predictive value 87.3%, negative predictive value 100%. For isolates with only have NDM, all values were determined as 100%. Two isolates with OXA-48 + NDM were interpreted as OXA-48-like by the combination disc test. Conclusion: Considering that OXA-48 is endemic in Turkey, the most common carbapenemase detected was OXA-48, an expected result. The combination disc test can be used for the detection of carbapenemase resistance genes in laboratories because of its inexpensive cost, ease of administration, ability to identify carbapenemase resistance mechanisms, and being highly compatible with polymerase chain reaction. Keywords: K. pneumoniae, Combination disc test, Carbapenemase, Carbapenem resistance, OXA-48