Antibiotic Susceptibility of Escherichia coli Strains Isolated in Community Acquired Urinary Tract Infections

Abstract

Escherichia coli is involved in 85{{}{%}{}} of community-acquired urinary tract infections (UTIs). For this reason, it is important to know its antimicrobial susceptibility patterns in order to give an appropriate empiric treatment of UTIs. The aim of this study is to evaluate the antibiotic resistance of E. coli strains isolated in community-acquired UTIs, and to see the prevalence of extended-spectrum {$}\beta{\$}-lactamase (ESBL) producing strains in the community. Methods: 2598 E. coli isolates were collected from outpatients with clinical evidence of community-acquired UTIs during the period January to November 2010 in a hospital in Madrid, Spain. Urine samples were cultured in CLED agar and incubated at 37°C for 48 hours. UTIs were defined as the culture of a single organism from a midstream urine specimen at ≥105 colony forming units per milliliter. Identification and antibiotic susceptibility tests were made by the routinely used automated system MicroScan (Siemens). Additionally, susceptibility tests were performed by disk diffusion method according to standard procedures. For the study, reduced susceptibility to 8 antibiotics commonly used in UTIs (amoxicillin, amoxicillin/clavulanic acid, cefuroxime, norfloxacin, ciprofloxacin, trimethoprim/sulfamethoxazole, fosfomycin and nitrofurantoin) was evaluated. In addition, extended-spectrum {$}\beta{\$}-lactamase (ESBL) production was examined; a ratio of 8 or greater for the ceftazidime to ceftazidime-clavulanic acid minimal inhibitory concentrations (MICs) and the cefotaxime to cefotaxime-clavulanic acid MICs was considered ESBL-positive. (Table presented). Results: 2598 E. coli isolates were obtained, 179 of which (6,9{{}{%}{}}) produced an extended-spectrum {$}\beta{\$}-lactamase. Isolates presenting reduced susceptibility to the different antibiotics evaluated are shown in the table attached. Conclusion: This study shows the increasing prevalence of ESBL-E. coli in community-acquired infections, being almost 7{{}{%}{}} of the E. coli strains isolated positive for ESBL. High resistance rates are obtained for quinolones (norfloxacin and ciprofloxacin) in both, ESBL and not ESBL producing E. coli. For this reason, these antibiotics should not be used for the empiric treatment of community-acquired UTIs in our country. However, low resistance rates are shown for nitrofurantoin and fosfomycin, in both ESBL and not ESBL E. coli, which suggests that these antibiotics may be a good option in the empiric treatment of UTIs.