Prevalence of Salmonella in beef cattle lymph nodes and the role of iron uptake proteins in Salmonella growth and survival in food products

  • Author / Creator
    Mushins, Aleicia
  • Salmonella enterica subspecies Enteritidis and Typhimurium are the cause of most cases foodborne salmonellosis. Salmonella is predominately found in poultry, beef and dairy products. It is an intracellular pathogen, known to enter the lymphatic system and it has been found in the lymph nodes of beef and dairy cattle, as well as in ground beef. Lymph nodes at risk of entering the food chain are located throughout the body and include, but are not limited to the superficial cervical, subiliac, superficial inguinal, popliteal, and mandibular. When inside lymph nodes, Salmonella is protected from the adverse effects of antibacterial sprays and desiccation of dry chilling in meat processing facilities. Superficial cervical, subiliac, superficial inguinal and deep popliteal lymph nodes were tested to determine presence or absence of Salmonella. None of lymph nodes tested (0/39) contained detectable levels of Salmonella. Feed samples were tested to determine presence or absence of Salmonella, as feed is a known vector. None of the feed samples (0/16) contained detectable levels of Salmonella. More sampling needs to be done to determine if cattle processors in Alberta need to be concerned about lymphatic infection by Salmonella. This research tentatively concludes that <2.7% of lymph nodes in cattle from Alberta are positive for Salmonella.

    Salmonella must survive in a broad range of environments: on vectors, in the gastrointestinal and lymphatic systems of cattle, on the food product, and in the GI tract of humans. A major factor in Salmonella’s ability to survive in a variety of different environments is its abundance of iron uptake systems. Salmonella has multiple ferrous iron uptake systems and it produces siderophores which uptake ferric iron. S. Enteritidis and S. Typhimurium and multiple iron uptake mutants of each serovar were used to determine the effect of each iron uptake gene on the growth and survival of Salmonella in broth, ground beef and UHT milk. A bacteriostatic effect was observed when S. Typhimurium 3128 ΔtonB, S. Typhimurium 3128 ΔiroNfepA, or S. Enteritidis 3346 ΔtonB was grown in UHT milk (a low iron environment). Gene expression data also showed that iroN and fepA were among the genes most upregulated in iron deficient environments. It may be possible to use an antimicrobial that interacts or blocks TonB or both IroN and FepA to prevent the growth of Salmonella in low iron foods. This strategy may be very important for preventing Salmonella infection.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Master of Science
  • DOI
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