Increased Mutation Frequencies in Escherichia coli Isolates Harboring Extended-Spectrum β-Lactamases

Hypermutable (mutation frequency [f], ≥4 × 10−8) Escherichia coli strains were more frequently found (43%) in a collection of 89 extended-spectrum β-lactamase (ESBL)-producing isolates from different patients (77 pulsed-field gel electrophoresis clones, 12 ESBL types) than in non-ESBL E. coli (26%) strains (P = 0.03). Among urinary tract isolates, the frequency of hypermutation was 40% in ESBL versus 26% in non-ESBL isolates (P = 0.03).