@article{a6fda210299a4612bae864dc8b9673f3,
title = "Population dynamics of enteric Salmonella in response to antimicrobial use in beef feedlot cattle",
abstract = "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.",
author = "Naomi Ohta and Norman, {Keri N.} and Bo Norby and Lawhon, {Sara D.} and Javier Vinasco and {Den Bakker}, Henk and Loneragan, {Guy H.} and Scott, {H. Morgan}",
note = "Funding Information: We acknowledge funding support by USDA-NIFA-AFRI (formerly CSREES; grant numbers 2008-35201-30235 and 2008-35201-04682) entitled: “Novel pre-harvest interventions to protect antimicrobials of critical importance in human and veterinary medicine” for the cattle field trial, while the subsequent phenotypic analysis was funded by USDA-NIFA-NIFSI (grant number 2010-51110-21083) entitled: “Practical interventions to effectively manage antibiotic resistance in beef and dairy cattle systems: a fully integrated approach.” Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture. Whole-genome sequencing of Salmonella isolates was funded by the National Cattlemen{\textquoteright}s Beef Association, a contractor to the Beef Checkoff. Technical assistance in the laboratory was provided by Ms. Roberta Pugh and Ms. Anisa Wakil. Dr. Barbara Gastel and Dr. Colin Young provided important feedback on earlier versions of this manuscript. Publisher Copyright: {\textcopyright} 2017 The Author(s).",
year = "2017",
month = dec,
day = "1",
doi = "10.1038/s41598-017-14751-9",
language = "English",
volume = "7",
journal = "Scientific Reports",
issn = "2045-2322",
publisher = "Springer Science and Business Media LLC",
number = "1",
}