Emergence of human pandemic O25:H4-ST131 CTX-M-15 extended-spectrum-β-lactamase-producing Escherichia coli among companion animals

Objectives: In view of the intercontinental emergence of Escherichia coli clone O25:H4-ST131 producing CTX-M-15 extended-spectrum b-lactamase (ESBL) in human clinical settings it would be of great interest to explore itsexistence in animals to unravel a possible reservoir function and the origin and transmission of this group ofmultiresistant strains.Methods: A total of 177 clinical phenotypically ESBL-producing E. coli isolates, mainly obtained from companionanimals with urinary tract infections, wound infections and diarrhoea, were collected in a veterinary diagnosticlaboratory covering a European-wide service area. They were screened for molecular subtype O25b and multilocussequence type 131. O25b-ST131 isolates were subsequently tested for ESBL types, and phenotypic andgenotypic resistance determinants. Further characterization of the strains was performed by PFGE and virulencegene typing.Results: Ten (5.6%) of 177 phenotypically ESBL-producing E. coli isolates, nine strains from dogs and one strainfrom a horse, were allocated to the B2-O25b-ST131 lineage. Nine of these isolates harboured a CTX-M-15-typeb-lactamase enzyme while one strain possessed an SHV-12-type ESBL. Macrorestriction analysis revealed acluster formation of six of the animal CTX-M-15-type ESBL-producing strains from five different Europeancountries together with a human control strain constituting a group of clonally related strains at a similarityvalue of 87.0%.Conclusions: Our findings demonstrate that the group of clonally related human B2-O25:H4-ST131 CTX-M-15-type ESBL-producing E. coli strains is present in companion animals from various European countries. This highlightsthe possibility of inter-species transmission of these multiresistant strains from human to animal and viceversa.