Spatiotemporal dynamics of β-lactam-resistant E. coli in young diseased calves in Wallonia, Belgium

Calves are one of the most common carriers of antibiotic-resistant bacteria among farm animals. However, the impact of antibiotic usage on resistance mechanisms, transmission routes between farms, and the transmission of resistant bacteria to humans remain largely unknown. Here we analyzed the population of {beta}-lactam resistant E. coli isolated over five calving seasons on 444 farms scattered throughout Wallonia, Belgium. Restrictions on critical antibiotics usage led to a reduction of resistance to 3rd generation cephalosporins but has no impact on population structure and {beta}-lactamase genes indicating a resilient population. The correlation between short genetic distances and geographic proximity suggests indirect transmission between farms by fomites with differences between regions east and west of the river Meuse. Phylogenetic analysis of calf isolates with isolates from public databases indicates transitions from bovine to human adaptation. These findings provide new means to further model the spread of E. coli in livestock farming.