Investigation of in-vitro efficacy of antibiotic combinations and presence of carbapenemases in multidrug-resistant Klebsiella pneumoniae isolates

Klebsiella pneumoniae is a major multidrug-resistant (MDR) bacterium. Combined use of antibiotics is one of the important choices in the treatment of these infections. In this study, it was aimed to evaluate the in vitro activity of colistin (COL), meropenem (MEM) and ceftazidime/avibactam (CZA) binary combinations against MDR K. pneumoniae clinical isolates and identifying carbapenemase genes. Between January 2022 and November 2023, randomly selected isolates isolated from pa-tient samples were included. Carbapenem resistance genes were investigated to 90 iso-lates by PCR. Additionaly, Carbapenem inactivation method (CIM) was used as a pheno-typic method in the investigation of carbapenemase production. Antimicrobial interac-tions were determined by checkerboard method. The most common gene was OXA-48 (72 isolates). KPC gene was detected in 10 isolates, NDM gene in 5 isolates. Synergy testing was performed on randomly selected isolates among isolates resistant to at least one of the COL, CZA, and MEM antibiotics. Synergistic effect was detected in 50% against COL-CZA, synergistic effect was detected in 75% against MEM-CZA and synergistic effect was detected in 45% against MEM-COL. The high synergy-partial synergy rates we detected suggested that COL-CZA, MEM-COL and MEM-CZA, may be effective treatment options for infections caused by MDR K. pneumoniae .