| dc.description.abstract | The occurrence of Salmonella in cattle has been well documented, but little
is known of tracking its prevalence and antimicrobial resistance (AMR) from postweaning
to slaughter. This study follows a longitudinal approach, allowing for the
best analysis of Salmonella prevalence and AMR in cattle. It was carried out to
monitor variation in Salmonella prevalence and AMR patterns in beef cattle from
range (calves post weaning in North Dakota (ND)) and feedlot cattle up to slaughter
(Nebraska). Two separate groups were analyzed, cattle which remained at the
Dickinson Research Extension Center (DREC) throughout the course of the study
and calves which initially were housed at the DREC, then transferred to a University
of Nebraska Feedlot, where they remained until slaughter. Fecal samples were
taken four times over a sampling period of eleven months, September 2008-July
2009; a mid-line sponge sample was taken of the steers before slaughter.
Laboratory culture of fecal and sponge samples for Salmonella followed a standard
published procedure. National Antimicrobial Resistance Monitoring System
(NARMS) panels were used for AMR testing of Salmonella isolates. Additionally,
PCR was performed to determine the prevalence of the lntegrase 1 gene in the
Salmonella isolates and presumptive integrase positive isolates were further
analyzed for the presence of a conserved sequence. Overall, the prevalence of
Salmonella ranged from 7.9% to 92.1% in adult cattle throughout the study. The
prevalence of Salmonella in calves at post weaning ranged from 27.7% to 54.4%,
with one month, December 2008, displaying 100% prevalence. At the final
sampling of calves, which included a midline sponge sample along with a fecal
grab, the prevalence of Salmonella was 45.8% and 46.8%, respectively. Salmonella
isolates displayed the highest rate of resistance towards chloramphenicol {57.3%),
streptomycin (54.7%) and tetracycline {54.7%) in both groups. Overall, the
integrase 1 gene was isolated from 100 (50.0%) isolates, with 88 (44.0%) isolates
harboring a conserved sequence. In conclusion, this study provided data on AMR
patterns of Salmonella shed by beef cattle at the different stages of production.
Also, an association between AMR towards the various antimicrobials tested and
presence of integrase 1 on the Salmonella isolates recovered was investigated
providing some information on the mechanisms of resistance to these
antimicrobials. However, further research is necessary to quantify other resistance
mechanisms that weren't explained by this study. Most importantly, this research
contributes information to the scientific literature on Salmonella prevalence and
AMR risk assessment in the beef cattle food chain that can allow for development
of appropriate control measures. | en_US |
