2012 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. 3.Progress Report: The food-borne pathogen Salmonella has been detected in the lymph nodes of cattle at harvest. Fat trim containing lymph nodes is a common component of ground beef and has been identified as a source of Salmonella in this commodity. Thus the objective of this research is to characterize variation in regional, seasonal and animal-type burden of Salmonella in lymph nodes of cattle presented at harvest. Sample collection for this project is not yet complete, however to date, lymph nodes have been collected from 1,712 carcasses from abattoirs located in five regions of the U.S. Overall Salmonella prevalence has been 3.9%, with cull and dairy cattle lymph nodes at 2.2% positive (n=537) and those of fed cattle at 4.6% positive (n=1175). Sample collection for this project will be completed in December 2012. Characterization of isolates is ongoing.