Population dynamics of enteric Salmonella in response to antimicrobial use in beef feedlot cattle. Academic Article uri icon


  • A randomized controlled longitudinal field trial was undertaken to assess the effects of injectable ceftiofur crystalline-free acid (CCFA) versus in-feed chlortetracycline on the temporal dynamics of Salmonella enterica spp. enterica in feedlot cattle. Two replicates of 8 pens (total 176 steers) received one of 4 different regimens. All, or one, out of 11 steers were treated with CCFA on day 0 in 8 pens, with half of the pens later receiving three 5-day regimens of chlortetracycline from day 4 to day 20. Salmonella was isolated from faecal samples and antimicrobial susceptibility was analysed via microbroth dilution. Serotype was determined by whole-genome sequencing. On day 0, mean Salmonella prevalence was 75.0% and the vast majority of isolates were pansusceptible. Both antimicrobials reduced overall prevalence of Salmonella; however, these treatments increased the proportion of multi-drug resistant (MDR) Salmonella from day 4 through day 26, which was the last day of faecal collection. Only six Salmonella serotypes were detected. Salmonella serotype Reading isolates were extensively MDR, suggesting a strong association between serotype and resistance. Our study demonstrates that the selection pressures of a 3rd generation cephalosporin and chlortetracycline during the feeding period contribute to dynamic population shifts between antimicrobial susceptible and resistant Salmonella.

published proceedings

  • Sci Rep

altmetric score

  • 0.5

author list (cited authors)

  • Ohta, N., Norman, K. N., Norby, B. o., Lawhon, S. D., Vinasco, J., den Bakker, H., Loneragan, G. H., & Scott, H. M.

citation count

  • 16

complete list of authors

  • Ohta, Naomi||Norman, Keri N||Norby, Bo||Lawhon, Sara D||Vinasco, Javier||den Bakker, Henk||Loneragan, Guy H||Scott, H Morgan

publication date

  • October 2017