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Identification and Characterization of Population(s) at Greatest Risk for Presences of Salmonella within Lymph Nodes

Loneragan, Guy; Brashears, Mindy
Texas Tech University
Start date
End date
Salmonella continues to be a significant public health burden and is the causative agent of over 1 million cases of foodborne illness each year. As a result of such infections, it is believed that 19,000 hospitalizations and 400 deaths occur annually. Therefore, it is important to focus research efforts on controlling this prominent microorganism in our food supply. It is well known that cattle harbor Salmonella in their gastrointestinal tracts and the microorganism can then be transferred to beef products, including ground beef. Science has proven that cattle feces present on their hides can contaminate the animal and, ultimately, their subsequent meat products. However, Salmonella can also be sequestered within the lymph nodes of cattle. These lymph nodes maybe present in the fat that is incorporated into ground beef. It is for these reasons that research into this issue is necessary if we are to protect our food supply. Needed are approaches to better understand the burden of Salmonella in the lymph nodes of cattle presented for harvest as well as potential mitigation strategies.

1. Quantify prevalence of Salmonella in lymph nodes of fed and cull dairy cattle.

2. Determine whether a commercially available Salmonella vaccine protects calves from lymph node colonization following significant oral challenge with Salmonella

More information
Study 1: Salmonella was readily recovered from subiliac lymph nodes, however regional and seasonal differences were observed. Prevalence was found to be highest in fed cattle from the Southern High Plains, averaging 15.9% and ranged from 29.5% positive in the fall of 2010 to 2.4% in the winter of 2011. Conversely, fed cattle from the Midwest showed a much lower prevalence rate, with only one of four sample events resulting in the observation of a lymph node containing Salmonella. Prevalence in lymph nodes of cull cattle from the High Southern Plains and the West Coast was generally low, on average 0.65% and 2.0%, respectively. Salmonella prevalence in lymph nodes of cull cattle from the Midwest was lowest, as none of the lymph nodes collected from cull cattle in this region were found to be contaminated with Salmonella.

Study 2: No significant treatment differences were observed in the percentage of lymph nodes positive for Salmonella Montevideo or Newport for Group 1. However at 21-d post- inoculation (i.e. Group 2), there were fewer (P<0.05) right popliteal (0 versus 75%) and right pre-scapular nodes (0 versus 75%) that were Salmonella positive in the Vaccine - Newport compared to Control - Newport treatments. The percentage of left popliteal and left pre-scapular nodes likewise tended (P=0.10) to decrease in the Vaccine-Newport treatment compared to non-vaccinated controls. Post-inoculation fecal samples were not affected by treatment for either strain. Initial and final body weights and overall body weight change were not different among treatments.

Funding Source
Nat'l. Cattlemen's Beef Assoc.
Project number
Natural Toxins
Bacterial Pathogens