DNA polymorphisms among Escherichia coli isolated from bacteriuric women

Restriction fragment length polymorphism (RFLP) patterns, plasmid profiles, and antimicrobial susceptibility patterns of paired sequential Escherichia coli isolates from antibiotic-treated and untreated elderly women were analyzed. Isolates from 26 of 27 subjects who were treated successfully with antibiotics but became reinfected differed by RFLP analysis, whereas 10 of 12 subjects who failed treatment and 11 of 14 untreated subjects had paired isolates with identical RFLP banding patterns. Only 40 of the 53 pairs of isolates could be analyzed by plasmid profiles; 36 of these 40 were concordant with RFLP analysis. Antimicrobial susceptibility patterns showed poor concordance with RFLP analysis. This study demonstrates the utility of RFLP analysis and indicates that isolation of E. coli from elderly women after sterilization of the urinary tract usually results from introduction of a new strain; elderly women who fail antibiotic therapy or receive no therapy may remain persistently infected with the same E. coli strain.