Translocation of orally inoculated Salmonella following mild immunosuppression in Holstein calves and the presence of the Salmonella in ground beef samples

Authors: WILKERSON, SHANNON - Auburn University; Broadway, Paul; Carroll, Jeffery - Jeff Carroll; Sanchez, Nicole; TIGUE, ALEX - Auburn University; REHM, JOHN - Auburn University; LAWHON, SARA - Texas A&M University; CALLAWAY, TODD - University Of Georgia; BRATCHER, CHRISTY - Auburn University

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2020
Publication Date: 5/5/2020
Citation: Wilkerson, S., Broadway, P.R., Carroll, J.A., Sanchez, N.C., Tigue, A., Rehm, J., Lawhon, S.D., Callaway, T.R., Bratcher, C.L. 2020. Translocation of orally inoculated Salmonella following mild immunosuppression in Holstein calves and the presence of the Salmonella in ground beef samples. Foodborne Pathogens and Disease. https://doi.org/10.1089/fpd.2019.2761.
DOI: https://doi.org/10.1089/fpd.2019.2761

Interpretive Summary: Salmonella is a food safety concern throughout the world and can contaminate products such as beef. While Salmonella primarily resides in the intestines of cattle, it can migrate to other tissues in muscle and fat that may be destined for human consumption. How these bacteria migrate and what triggers them to migrate is relatively unknown. Previous research in our lab with pigs suggested that when the immune system of an animal is weakened, the bacteria may spread more rapidly. Scientists from the USDA-ARS Livestock Issues Research Unit, the University of Auburn, and the University of Georgia teamed up determine if artificially weakening the immune system of calves prior to infection with Salmonella, changed the way Salmonella moved throughout the body. Results from this study revealed that whether or not the immune system was weakened similar amounts of Salmonella was still found in most tissues. Also in this study, joint fluid was sampled and Salmonella was discovered in some joints. When processing a beef carcass, many joints are broken, and the fluid, if contaminated with Salmonella, has the potential to contaminate the meat, knives, and other equipment, and may contaminate tens of thousands of pounds of other meat products. Overall, this study proved that ingestion of Salmonella can spread rapidly throughout healthy and sick calves and affect food safety. This information is important to food processors and consumers as they work to maintain a safe food supply and eliminate the potential for Salmonella to enter the food chain and reduce the risk of foodborne illness.

Technical Abstract: The objective of this study was to determine if immunosuppression via daily dexamethasone infusion altered Salmonella translocation from the gastrointestinal tract. Weaned Holstein steers (n = 20; BW = 102 ± 2.7 kg) received dexamethasone (DEX: n = 10; 0.5 mg/kg BW) or saline (CON; n = 10; 0.5 mg/kg BW) for 4 d (from d -1 to d 2) prior to oral inoculation of naldixic acid resistant Salmonella Typhimurium (SAL; 3.4x106 CFU/animal) on d 0. Fecal swabs were obtained daily, and blood was collected for hematology. Upon harvest (d 5), the ileum, cecal fluid, lymph nodes (ileocecal, mandibular, popliteal, and subscapular), and synovial (stifle, coxofemoral and shoulder) swabs were collected for the isolation of the inoculated strain of SAL. White blood cell and neutrophil concentrations were elevated (P < 0.01) in DEX following an administration event. Following inoculation, 100% of DEX calves shed the experimental strain of SAL for 5 d, 90% of CON calves shed from d 1 to 3, and 100% of CON calves shed from d 4 to 5. Greater (P < 0.01) concentrations of SAL were quantified from the cecum of DEX calves (3.86 ± 0.37 log CFU/g) than CON (1.37 ± 0.37 log CFU/g). There was no difference in SAL concentrations between DEX and CON calves in ileal tissue (P = 0.07), nor ileocecal (P = 0.57), mandibular (P=0.12), popliteal (P= 0.99), or subscapular (P = 0.83) lymph nodes. Of the stifle samples collected, 3.3% were positive for SAL highlighting contamination opportunity during hind quarter fabrication. While more research is needed to elucidate the interactions of immunosuppression and pathogen migration patterns, these data confirm that orally inoculated SAL can translocate from the gastrointestinal tract and be harbored in atypical locations representing a food safety risk.