Determination of intravenous fosfomisin resistance in clinical insulations of escherichia coli by agar dilution method and investigation of the synergist effect with meropenem, gentamycin, ceftriaxone antibiotics

Due to the limited use of antibiotics for the treatment of carbapenem resistant Enterobacterales, combination therapy regimens have recently come to the fore. In our study, fosfomycin resistance rates and combination interactions of meropenem, gentamicin and ceftriaxone antibiotics were investigated by using agar dilution method in carbapenem resistant Escherichia coli isolates. Sixty carbapenem-resistant Escherichia coli strains isolated from various samples (urine, blood, aspirate, wound, cerebrospinal fluid, endotracheal aspirate) sent to Dicle University Medical Faculty Hospitals Medical Microbiology Laboratory from patients in clinical and intensive care units were included in our study. MALDI Biotyper 3.1 (Bruker Daltonics, ABD )was used for species identification. Antibiotic susceptibility tests and carbapenem resistance status of the strains were studied with BD Phoenix (Becton Dickinson Diagnostics). Ertapenem, imipenem and meropenem disc diffusion tests were used to confirm carbapenem resistance. By agar dilution method, %76.6 of the strains were resistant to fosfomycin, %61.6 to meropenem, %85 to gentamicin %, 98.3 to ceftriaxone. % 35 of the isolates were found to be synergistic in the fosfomycin and meropenem combination, %33.4 in the fosfomycin and gentamycin combination, and %1.7 in the fosfomycin and ceftriaxone combination. Antagonism was detected in the combination of fosfomycin-meropenem in only one strain. In our study, the synergy rate of meropenem and gentamicin antibiotics was found to be high. More research is needed before the antibiotics used in the combination study can be used clinically in combination.