Abstract:
Introduction: A new approach to carbapenem resistance-K. pneumoniae infections is to use combination drug therapies. However, little data are available about the effectiveness of the in vitro carbapenem plus colistin combination against oxacillinase-48 (OXA-48) producing K. pneumoniae. Therefore, the aim of this study is to assess the potential synergistic activity of imipenem plus colistin in OXA-48-producing K. pneumoniae strains and investigate the changes in the imipenem minimal inhibitory concentrations (MICs) to varying MICs of colistin. Materials and Methods: Carbapenem and colistin resistance (ColR) genes were investigated by polymerase chain reaction. In the first stage, synergistic properties were determined by the checkerboard combination method. In the second step, at varying colistin concentrations, changes in the imipenem MICs were investigated. Results: Colistin MIC502 μg/ml, MIC9016 μg/ml, and imipenem MIC5032 μg/ml, MIC90128 μg/ml were found, respectively. According to the fractional inhibitor concentration (FIC) formula, 62.2% of the isolates were synergistic, and 37.8% were indifference. When the colistin was fixed at 0.125 μg/ml, 0.25 μg/ml, 0.5 μg/ml, 1 μg/ml, and 2 μg/ml, respectively. Significant decreases were observed in the imipenem MICs, especially of colistinsensitive isolates. However, imipenem MICs of ColR isolates did not decrease to susceptible levels. Conclusion: This information will facilitate the design of antibiotic regimens that are more suitable for treating infections due to such pathogens producing OXA-48 and prolong these antibiotics' efficacy. Further in vitro research is required to determine which treatment combination is best and its optimal use as combination therapy to treat these infections. © Copyright 2021 by the Infectious Diseases and Clinical Microbiology Specialty Society of Turkey Mediterranean Journal of Infection, Microbes and Antimicrobials published by Galenos Yayinevi.