Animal Sciences Masters Theses

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Browsing Animal Sciences Masters Theses by browse.metadata.program "Veterinary and Microbiological Sciences"

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    Characterization of Salmonella spp. Isolated From Beef Cattle Post-Weaning To Slaughter
    (North Dakota State University, 2010) Nesemeier, Brenton Fred
    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.