Within-farm dynamics of ESBL/AmpC-producing Escherichia coli in veal calves: a longitudinal approach

Objectives: To assess the within-farm dynamics of extended-spectrum beta-lactamase (ESBL)/AmpC-producing Escherichia coli in veal calves. Methods: Three veal-calf fattening farms were screened. Faecal samples from all calves within a compartment (109-150 per farm) were taken upon arrival on the farm (T0) and after 3, 6, 8 and 10 weeks (T3-T10). ESBL/AmpC genes were characterized by PCR and sequencing. Plasmids were characterized by transformation, PCR-based replicon typing and plasmid multilocus sequence typing (MLST). E. coli genotypes were analysed by MLST. Results: At T0 the prevalence of ESBL/AmpC-producing E. coli ranged from 18% to 26%. These were predominantly isolates carrying bla(CTX-M-1) and bla(CTX-M-15) genes, located on various plasmids and E. coli sequence types (STs). Farm 1 was negative for ESBL/AmpC-producing E. coli after T0. Farm 2 showed an increase up to 37% at T3, which subsequently decreased gradually to 0% at T10. The presence from T3 to T10 on farm 2 was mainly caused by the clonal spread of a multiresistant E. coli ST57 harbouring bla(CTX-M-14) on an IncF F2:A-:B- plasmid. Farm 3 showed a gradual decrease in prevalence to 1.4% at T10, with a relative increase of the identical clonal variant as shown for farm 2. A second clonal variant found in farm 3 was a multiresistant E. coli ST10 harbouring bla(CTX-M-14) on an IncK plasmid. Conclusions: The prevalence of ESBL/AmpC-producing E. coli decreased over time. Aclonal spread was observedon farm 2 and farm 3, illustrative of the complex dynamics probably associated with the use of antimicrobials.