2013 Annual Report
1a.Objectives (from AD-416):
Bovine peripheral lymph nodes, including subiliac lymph nodes, have been identified as a potential source of Salmonella, when trim containing these nodes is incorporated into ground beef. In order to gain a better understanding of the potential risk to human health imposed by Salmonella harborage in subiliac lymph nodes of fed and cull cattle at harvest, it is important to characterize the variation in regional, seasonal, and animal-type burden of Salmonella in these tissues. In the proposed study, we will examine the biology, epidemiology and ecology of Salmonella in bovine lymph nodes. The information gathered in these studies will be used to explore candidate control strategies and identify those that are most successful and adoptable.
1b.Approach (from AD-416):
Lymph nodes will be collected from cattle at harvest (n=1,200 per year). Lymph node samples will be trimmed, surface sterilized, enriched and analyzed for the presence of Salmonella. Salmonella will be enumerated from a subset (yet to be determined) of lymph node samples. Salmonella isolated will be characterized as to serotype and antimicrobial susceptibility phenotype. A subset of Salmonella isolated will undergo molecular characterization including pulsed field gel electrophoresis (PFGE) phenotyping, plasmid profiling, and genome/transcriptome sequencing.
The data collected show subiliac lymph nodes can be a significant source of Salmonella, if incorporated in ground beef, and that prevalence appears to be affected by season, region and animal type. The data further show that contaminated nodes can carry substantial levels of Salmonella (3.0 to >4.8 log^10^ CFU/lymph node). Given that lymph node harborage protects Salmonella from carcass interventions, research is needed to define opportunities for mitigating the risk of Salmonella contamination in lymph nodes of apparently healthy cattle.