Comparative antimicrobial resistance and genomic diversity of Escherichia coli isolated from urinary tract infections in the community and in hospitals.

Well-defined community- and nosocomially-acquired isolates of Escherichia coli responsible for urinary tract infections were studied for their resistance to beta-lactams, quinolones, and co-trimoxazole, antibiotics widely used for treatment of urinary infections. For each strain, an antibiogram was obtained using the Vitek automat, which estimates the minimal inhibitory concentrations of various drugs. Nosocomial strains were significantly more amoxycillin-resistant than community strains (P = 0.01) and were also significantly more resistant to co-trimoxazole (P = 0.025) and first generation quinolones (P = 0.02) than the latter. To determine whether this was due to transmission of strains within the hospital, DNA restriction patterns, established using XbaI enzyme and separation by pulsed-field gel electrophoresis, were compared. Extreme genomic diversity was found among both the community and nosocomial strains. The increased frequency of resistance among nosocomial strains is thus not due to transmission of resistant hospital strains but probably results from the selection of resistant strains from the endogenous flora of patients.