Salmonella recovery from chicken bone marrow and cecal counts differ by pathogen challenge method

Mechanically separated chicken (MSC) may be incorporated into other further processed foods, and has been identified as a transmission vehicle in human foodborne disease outbreaks involving the pathogen Salmonella enterica. Chickens possess pneumatic bones producing marrow, which may become infected with Salmonella and present a mechanism for Salmonella contamination of MSC. The primary objective of the current study was to ascertain whether chicken bone marrow was susceptible to Salmonella infection as a function of pathogen challenge method. Additionally, this study sought to determine the impact of Salmonella challenge site and inoculation on subsequent numbers of the microorganism in the cecum at 3, 6 and 9 d post-challenge. In this study, 30-day-old birds (Gallus domesticus) were separately challenged with S. enterica by one of the 6 experimental treatment methods: oral or endo-tracheal gavage, and transdermal scratch challenge on the breast or back muscles, with or without feathers (N = 150). Differing Salmonella recovery rates were detected in bone marrow from euthanized birds (P = 0.0015); oral and endo-tracheal gavage produced Salmonella recovery frequencies of 10% and 20%, respectively. Counts of Salmonella from chicken cecal samples statistically differed as a function of challenge method (P = 0.032); the highest numbers of Salmonella in cecal samples were obtained from orally gavaged birds (3.0 log10 cfu/g). Study results demonstrate the potential for chickens to contract short-term systemic infection following Salmonella challenge using methods of pathogen challenge simulating aerosol inhalation, ingestion, or wounding. Salmonella entry into chicken bone marrow may result in decreased likelihood of Salmonella performance standard compliance and increased pathogen transmission risk to consumers.