Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Microbiology and Preventive Medicine

First Advisor

Ronald Griffith


The overall objectives of this research were to first determine the overall prevalence of S. enterica in a given population of cull sows, secondly to apply control measures to lower the prevalence of S. enterica , thirdly was to use epidemiological tools to investigate the origin of S. enterica serovars isolated from the farm, live hog market, and abattoir, and lastly to determine invasiveness of S. enterica serovars isolated from cull sow feces, tissues, and environmental samples, as measured by an invasion assay.;The total average percent positive fecal samples at the farm, the live hog market, and abattoir were 3% (5 of 181), 2% (3 of 181) and 41% (74 of 180), respectively. There were 12 serotypes recovered at the abattoir that were not previously encountered at the farm or live hog market. S. enterica was isolated from 44% (35 of 80) of no-hold sows compared to 59% (47 of 80) of sows held in lairage. For no-hold sows, 39% (31 of 80) of cecal contents yielded S. enterica compared to 55% (44 of 80) of cecal contents from held sows. Seven different S. enterica serovars isolated from the abattoir pen floor prior to occupancy by cull sows.;There were high levels of resistance to streptomycin and tetracycline. Of all the serovars tested, we found S. derby had the highest frequency of resistance to multiple antibiotics (>2). Matches were found between S. enterica serovars having the same antimicrobial resistance profiles at the farm, abattoir, and chopped meat batch. We isolated invasive S. enterica strains from different animals and tissues. Invasive serovars isolated in the lymph nodes (the ventral thoracic and subiliac lymph nodes), could then be recovered in the meat block containing tissues with lymph nodes in them.;These preliminary findings indicate that chopped meat blocks may be contaminated from S. enterica infected lymph nodes or isolates that survive the lactic acid carcass wash from fecal contamination on carcass sides. Future research should focus on interventions to reduce the prevalence of tissues containing pathogenic S. enterica and the environment (abattoir pens) where swine may be infected.



Digital Repository @ Iowa State University,

Copyright Owner

Steven Thomas Larsen



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File Size

118 pages