The changing prevalence of drug-resistant Escherichia coli clonal groups in a community: evidence for community outbreaks of urinary tract infections

Abstract

A multidrug-resistant clonal group (CgA) of Escherichia coli was shown to cause half of all trimethoprim-sulphamethoxazole (TMP-SMZ)-resistant urinary tract infections (UTIs) in a college community between October 1999 and January 2000. This second study was conducted to determine the fate of CgA. Urine E. coli isolates from women with UTI, collected between October 2000 and January 2001, were tested for antibiotic susceptibility, O serogroup, ERIC2 PCR and DNA macrorestriction patterns using pulsed-field gel electrophoresis. The proportion of UTIs caused by CgA declined by 38% (P<0.001) but the prevalence of resistance to TMP-SMZ did not change. Six additional clonal groups were identified and these were responsible for 32% of TMP-SMZ-resistant UTIs. The temporal decline in the proportion of UTIs caused by CgA provides evidence that CgA caused a community outbreak of UTI. The fluctuation and occurrence of other E. coli clonal groups in this community suggest that a proportion of community-acquired UTIs may be caused by E. coli disseminated from one or more point sources.

Fig. 1

ERIC2 PCR patterns of TMP–SMZ-resistant, clonal group A (CgA) and ciprofloxacin-TMP–SMZ-resistant E. coli UTI isolates. Lanes 1 and 12, 1 kb ladder; lane 2, CgA prototype isolate and positive control; lanes 3–6, putative CgA isolates; lanes 7–11, ciprofloxacin-TMP–SMZ-resistant isolates, including CgG (lanes 7–9); lane 13, negative control. All isolates were recovered from unique women, except 1792 (lane 4) and 2000 (lane 5), which were isolated from two UTI episodes in the same woman, 57 days apart.

Fig. 2

XbaI PFGE patterns of clonal group A (CgA) and ciprofloxacin-TMP–SMZ-resistant CgG isolates from the phase II study. Lanes 1 and 10, lambda ladder; lane 2, prototype CgA isolate; lanes 3–6, putative CgA isolates; lanes 7–9, ciprofloxacin-TMP–SMZ-resistant CgG isolates.

Fig. 3

XbaI PFGE patterns of CgC isolates from the phase II study. Lanes 1 and 10, lambda ladder; lanes 2–9, CgC isolates. Lanes 3, 7 and 9 exhibit indistinguishable patterns, as do lanes 4 and 8.

Fig. 4

XbaI PFGE patterns of CgD isolates from the phase II study. Lanes 1 and 10, lambda ladder; lanes 2–9, CgD isolates. Two pairs of women were infected by strains with indistinguishable PFGE patterns (see text).