EPIDEMIOLOGY, ECOLOGY, AND MOLECULAR GENETICS OF ANTIMICROBIAL RESISTANCE IN PATHOGENIC AND COMMENSAL BACTERIA FROM FOOD ANIMALS
Location: Bacterial Epidemiology and Antimicrobial Resistance
Title: Epidemiology of Food-borne Salmonella in Poultry
Submitted to: Western Poultry Disease Conference
Publication Type: Abstract Only
Publication Acceptance Date: March 22, 2009
Publication Date: March 22, 2009
Citation: Cray, P.J., Berrang, M.E., Cox Jr, N.A., Richardson, L.J. 2009. Epidemiology of Food-borne Salmonella in Poultry. American College of Poultry Veterinarians and Western Poultry Disease Conference. Sacramento, CA. March 22-25,2009. P-11.
Despite decades of research and implementation of numerous control measures, Salmonella continues to colonize all vertebrates. In food producing animals, Salmonella can be transferred to humans via contaminated food stuffs or through contact with (ill) animals. Environmental contamination plays a role in colonization, persistence, and transmission within animals and man. There are over 2500 different serotypes of Salmonella and some appear to have predilection for colonization of certain animal species over others. From processed broiler carcasses, the top 5 serotypes as reported from the National Antimicrobial Monitoring System are S. Kentucky, S. Heidelberg, S. Typhimurium var. 5-, S. Enteritidis and S. Typhimurium. In contrast, the top 5 serotypes from processed turkey carcasses are S. Heidelberg, S. Hadar, S. Seneftenberg, S. Reading and S. Saintpaul. Each serotype exhibits different characteristics, particularly with respect to colonization, persistence and antimicrobial resistance.
Studies on Salmonella ecology in poultry pre-harvest has led to implication of numerous sources as vectors for introduction of the organism into poultry flocks (i.e. papers pads,, worker boots, litter, birds and pests (including flies and beetles)). Internal colonization is complex and variable by serotype. Sequestration of bacteria in certain internal organs may increase survival within the host. Additionally, the presence of specific virulence attributes may affect colonization. While recovery is highest after placement on-farm, Salmonella can persist throughout grow-out resulting in isolation from the ceca at the plant. However, serotypes readily found on-farm do not always correlate with serotypes recovered from the plant; transport plays a significant role in cross-contamination. At the plant, pre-chill counts are typically higher than post-chill counts and the reduction in both numbers and prevalence post-chill is attributed to interventions in the chill tank among others.
Of particular interest is the recent ability to track serotype/strain movement in ‘farm-to-fork’ studies. The importance of strain subtyping cannot be emphasized enough. It is not uncommon to observe significant genotype differences among isolates of the same serotype; phenotype among isolates does not necessarily correlate with molecular type. Molecular typing tools become particularly useful in food-borne outbreaks. Collectively, the epidemiology of Salmonella is dynamic, complex, and evolving. However, by combining molecular and phenotype characterization, our ability to develop more effective control programs can be enhanced.