High resistance prevalence towards ampicillin, co-trimoxazole and ciprofloxacin, among uropathogenic Escherichia coli isolates in Mexico City

Abstract

Background : The prevalence of antimicrobial resistance among uropathogenic E. coli varies widely worldwide; to guide empirical therapy is necessary to have local, up-to-date susceptibility data. Methodology: We tested 907 isolates from patients in Mexico City by disk diffusion and further characterized ciprofloxacin, cephalosporin and nitrofurantoin resistant strains. Results: Isolates were mostly resistant to ampicillin (74%), trimethoprim-sulfamethoxazole (60.1%) and ciprofloxacin (32.6%). The most effective drug was netilmicin (5.1% resistant) and the most effective of oral drugs was nitrofurantoin (7.4% resistant). Sixty-percent of ciprofloxacin-resistant strains had minimal inhibitory concentrations of 125 μg/ml or higher, well beyond urinary concentrations at the end of the 12-hour inter-dose period for standard oral regimes. Extended-spectrum beta-lactamases were detected in 6% of strains, most of them from community-acquired infections. All strains resistant to nitrofurantoin carried a ~20 Kb plasmid, which when transformed into a susceptible recipient, conferred resistance to nitrofurantoin, ampicillin, sulfonamides, streptomycin, and partially protected against ciprofloxacin. Conclusions: Drugs considered of choice against uncomplicated urinary tract infections are facing high resistance prevalences and resistance determinants formerly seen only at hospitals are now among community strains. Treatment guidelines from developed countries might not reflect these local trends.