Comparative virulotyping of extended-spectrum cephalosporin-resistant E. coli isolated from broilers, humans on broiler farms and in the general population and UTI patients

During the last decade extended-spectrum cephalosporin (ESC)-resistant Escherichia coli from food-producing animals, especially from broilers, have become a major public health concern because of the potential transmission of these resistant bacteria or their plasmid-encoded resistance genes to humans. The objective of this study was to compare ESC-resistant E. coli isolates from broilers (n = 149), humans in contact with these broilers (n = 44), humans in the general population (n = 63), and patients with a urinary tract infection (UTI) (n = 10) with respect to virulence determinants, phylogenetic groups and extended-spectrum β-lactamase (ESBL)/plasmidic-AmpC (pAmpC) genes. The most prevalent ESBL/pAmpC genes among isolates from broilers and individuals on broiler farms were blaCTX-M-1, blaCMY-2 and blaSHV-12. In isolates from humans in the general population blaCTX-M-1, blaCTX-M-14 and blaCTX-M-15 were found most frequently, whereas in UTI isolates blaCTX-M-15 predominated. The marker for enteroaggregative E. coli, aggR, was only identified in a broiler and human isolates from the general population. The extraintestinal virulence genes afa and hlyD were exclusively present in human isolates in the general population and UTI isolates. Multivariate analysis, based on ESBL/pAmpC resistance genes, virulence profiles and phylogenetic groups, revealed that most UTI isolates formed a clearly distinct group. Isolates from broilers and humans associated with broiler farms clustered together. In contrast, isolates from the general population showed some overlap with the former two groups but primarily formed a separate group. These results indicate than transmission occurs between broilers and humans on broiler farms, but also indicate that the role of broilers as a source of foodborne transmission of ESC-resistant E. coli to the general population and subsequently causative agents of human urinary tract infections is likely relatively small.