Integron-mediated ESBL resistance in rare serotypes of Escherichia coli causing infections in an elderly population of Israel

Objectives: To identify and characterize the aetiology of an outbreak of extra-intestinal multidrug-resistant Escherichia coli infections in elderly patients in Israel. Methods: Extended-spectrum β-lactamase (ESBL)-producing clinical isolates of E. coli from extra-intestinal sources were tested for susceptibility to non-β-lactam drugs, and their serotypes were determined. Restriction enzyme digestion, followed by PFGE of DNA purified from isolates, was used to classify the phylogenetic relationship between them. Plasmid DNA from five isolates of different serotypes was used to transform an E. coli laboratory strain. The plasmids were partially sequenced. Results: E. coli isolates from 86 patients, mostly elderly, were shown to be positive for inhibitor-susceptible ESBLs, and more resistant to cefotaxime than to ceftazidime. Ninety-six per cent of ESBL producers were also resistant to gentamicin, and 100% to trimethoprim/sulfamethoxazole and ciprofloxacin. All isolates belonged to one of five serotypes. PFGE analysis of purified DNA yielded 17 profiles. Sequencing of plasmids isolated from the transformants identified sul1, aac(6′)-lb and bla_CTX-M-2. These genes were embedded in an integron, InS21. Conclusions: Extra-intestinal infections with ESBL-producing E. coli of different serotypes and probably mixed clonality showed a surprising homogeneity in resistance profiles, with 100% being co-resistant to ciprofloxacin and trimethoprim/sulfamethoxazole, and 96% to gentamicin. Plasmid DNA from three isolates from different serotypes contained integron InS21, previously demonstrated in Salmonella enterica from Argentina. This is the first molecular identification of an ESBL gene and integron in Israel or neighbouring geographical areas.