Molecular characterization of blaESBL-producing Escherichia coli cultured from pig farms in Ireland.

OBJECTIVES: To characterize ESBL-encoding Escherichia coli cultured from pigs and their plasmids carrying these genes following conjugation into recipient strains.

METHODS: Six ESBL-producing E. coli were recovered from faecal samples taken from pigs along with a further isolate from the environment of a farrowing house on three pig farms in Ireland. These isolates were characterized by phylogenetic grouping, MLST and ESBL genotype analyses. Conjugation experiments were carried out in broth mating assays. S1-nuclease PFGE was used to determine the plasmid profiles. Whole-genome sequences of the seven E. coli were determined and subsequently analysed.

RESULTS: Phylogenetic groups and the corresponding MLST STs identified among the seven tested E. coli isolates included A/ST10, A/ST34, C/ST23 and C/ST1629. All seven isolates carried one or more high-molecular-weight plasmids and demonstrated the ability to transfer their cefotaxime resistance phenotype at high frequencies. Five transmissible plasmid replicon types were detected, including IncK/B (n = 3), IncI1 (n = 2), IncFIA (n = 1), IncFIB (n = 1) and IncN (n = 1). ESBL-encoding genes, including blaCTX-M-14 , blaCTX-M-15 and blaTEM-20 , were identified.

CONCLUSIONS: As the first report from pig sources in Ireland, characterization of these ESBL-encoding isolates and their transmissible plasmids extends our understanding on these resistance markers from porcine E. coli.