The effect of Enterococcus faecium M74 feed additive on the extended-spectrum beta-lactamases/AmpC-positive Escherichia coli faecal counts in pre-weaned dairy calves

The increasing occurrence of extended-spectrum beta-lactamases and/or AmpC-positive Escherichia coli among different species of food producing animals poses a threat to public health. The animal gut plays a key role in the development of antibiotic resistant bacteria, allowing the selection, multiplication and subsequent contamination of the farm environment. However, applicable procedures for reducing such bacteria on farms are currently unavailable. The present study was aimed to determine whether a probiotic administration to new-born dairy calves would reduce faecal shedding of extended-spectrum beta-lactamases and/or AmpC-positive Escherichia coli during the pre-weaning period. Ten randomly assigned new-born Holstein calves on a dairy farm with recent evidence of high occurrence of AmpC-positive Escherichia coli among calves were treated by a probiotic mix within 12 h after birth. Nine control calves were not treated. Faecal samples were collected from each calf daily on days 2 through 5, and then on days 7, 10, and 14. The faecal samples were cultured, and the mean numbers of cefotaxime-resistant Escherichia coli and confirmed enteroaggregative Escherichia coli were compared between the two groups. Results suggested that the Enterococcus faecium probiotic treatment (Enterococcus faecium M74, NCIMB 11181) of new-born calves did not reduce the enteroaggregative Escherichia coli counts in their faeces. There was no significant difference in the shedding of enteroaggregative Escherichia coli between the probiotic-treated and control calves throughout the two-week study period.