Fosfomycin: In Vitro Evaluation of Resistance in Escherichia coli Isolates from Hospitalized Patients in ICUs

Background and Objectives: Urinary tract infection is a common nosocomial infection that has recently become difficult to treat because of the increased emergence of multi-drug resistant strains. In this study, we aimed to determine the minimum inhibitory concentration of fosfomycin in multi-drug resistant Escherichia. coli strains, isolated from hospitalized patients with urinary tract infection in intensive care unit (ICU) and coronary care unit (CCU). Materials and Methods: In this descriptive cross-sectional study, patients (n =106) in ICUs were studied. After identifying E. coli isolates using specific tests, broth microdilution test was used in according to CLSI M100-S25 (2015) criteria to determine the minimum inhibitory concentration (MIC) of fosfomycin. Result: Frequency of E. coli isolates was 62.3%, most of which had been isolated from ICU patients (56.5%). Determined MIC of fosfomycin showed that 85% of the strains were susceptible to it (MIC, ≤64μg/mL). The concentration of fosfomycin, that inhibited 90% growth of isolates (MIC90) was 16μg/mL, 4-folds lower than enoxacin, tetracycline, gentamicin (MIC90=64μg/mL), 2-folds lower than imipenem, cefprozil, cefoxitin (MIC90=32μg/mL) and 8-folds lower than piperacillin (MIC90=128μg/mL). Conclusion: Our results indicate the high antimicrobial activity of fosfomycin against uropathogenic E. coli isolates and more potent in vitro activity than the other agents.