Susceptibility of Extended-Spectrum Beta-Lactamase-Producing Escherichia coli Urine Isolates to Fosfomycin, Ciprofloxacin, Amikacin and Trimethoprim-Sulfamethoxazole

Aim: Urinary tract infections (UTIs) caused in particular by extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli strains are related with high morbidity and mortality, and treatment is quite difficult. These infections generally are treated by carbapenems, and their costs are high. We aimed in this study to investigate the susceptibilities of ESBL-producing E. coli strains isolated from urine cultures to fosfomycin, ciprofloxacin, amikacin and trimethoprim-sulfamethoxazole and to determine the general resistance profile in our region of these strains isolated from UTIs.Materials and Methods: Between January 2005-December 2005, ESBL-producing E. coli strains isolated from urine samples sent from various outpatient and inpatient clinics to the Bacteriology Laboratory of the Department of Microbiology and Clinical Microbiology were included prospectively in the study. ESBL production was detected using the double disk synergy test. Antibiotic susceptibility testing was performed for ESBL-producing isolates by disk diffusion test according to Clinical and Laboratory Standards Institute (CLSI)criteria. Escherichia coli ATCC 35218 and ATCC 25922 were used as control strains. The diagnosis of nosocomial UTIs was established according to the Centers for Disease Control and Prevention criteria. The datawere assessed using the SPSS 11.0 packet program.Results: A total of 344 ESBL-producing E. coli isolates (241 nosocomial isolates; 103 outpatient isolates)were included in the study. The rates of resistance were 3.5% for fosfomycin, 76.5% for ciprofloxacin, 11%for amikacin, and 74.4% for trimethoprim-sulfamethoxazole. While resistance rates of nosocomial strains were 4.1%, 81.3%, 11.2%, and 71%, respectively, resistance rates of the strains isolated from outpatients were 1.9%, 65%, 10.7%, and 82.5%, respectively. There were statistically significant differences between the two groups for ciprofloxacin and trimethoprim-sulfamethoxazole.Conclusions: Because of the high antibiotic resistance rates in our country, we think that fosfomycin and amikacin may have priority in the treatment of non-complicated UTIs caused by ESBL-producing E. coli strains due to ease of use and high concentration in the urine.