Dendrogram ofXbaI pulsed-field gel electrophoresis (PFGE) profiles forEscherichia coliisolates. One representative of each PFGE type per subject was included in the dendrogram, which includes extended-spectrum β-lactamase-producing E. coli (ESBL-EC) (n = 35) isolates, plus reference strains representing UK Strains A and D, and international pulsotype labelled USA Control 812. Reference strains with ≥ 85% profile similarity to study isolates are shown. The dendrogram was generated using the unweighted pair group method with arithmetic mean (UPGMA) algorithm based on Dice similarity coefficients. Two PFGE clusters (A and B) were defined based on ≥ 85% profile similarity. Isolates labelled “ESBL E. coli” represent ESBL-EC.