CTX-M-1- and CTX-M-15-type β-lactamases in clinical Escherichia coli isolates recovered from food-producing animals in France

Clinical Escherichia coli strains with resistance or variable susceptibility to third-generation cephalosporins were detected in cattle, swine and poultry in France. These strains were shown to produce extended-spectrum β-lactamases (ESBLs), with CTX-M-1- and CTX-M-15-type β-lactamases being responsible for this phenotype. The blaCTX-M-1 gene was encountered most commonly and was characterised in seven E. coli strains isolated from cattle, swine and poultry, whereas blaCTX-M-15 was identified in one E. coli isolated from cattle. These genes were located on a conjugative plasmid and were linked to the insertion sequence ISEcp1, which could have contributed to dissemination of the resistance gene. No epidemiological link between the strains was determined by pulsed-field gel electrophoresis, although two plasmids were identical in two strains isolated from swine and in two strains isolated from cattle and poultry. Thus, this study describes the emergence of ESBLs in animals in France, with a probable similar prevalence rate to that observed in humans. This is a major concern because of the possibility of transfer of these genes between animal species as well as to humans, leading to treatment failures in veterinary and human medicine.