Abstract
BackgroundSalmonellosis is one of the most important bacterial food borne illnesses worldwide. A major source of infection for humans is consumption of chicken or egg products that have been contaminated with Salmonella enterica serotype Typhimurium, however our knowledge regarding colonization and persistence factors in the chicken is small.ResultsWe compared intestinal and systemic colonization of 1-week-old White Leghorn chicks and Salmonella-resistant CBA/J mice during infection with Salmonella enterica serotype Typhimurium ATCC14028, one of the most commonly studied isolates. We also studied the distribution of wild type serotype Typhimurium ATCC14028 and an isogenic invA mutant during competitive infection in the cecum of 1-week-old White Leghorn chicks and 8-week-old CBA/J mice. We found that although the systemic levels of serotype Typhimurium in both infected animal models are low, infected mice have significant splenomegaly beginning at 15 days post infection. In the intestinal tract itself, the cecal contents are the major site for recovery of serotype Typhimurium in the cecum of 1-week-old chicks and Salmonella-resistant mice. Additionally we show that only a small minority of Salmonellae are intracellular in the cecal epithelium of both infected animal models, and while SPI-1 is important for successful infection in the murine model, it is important for association with the cecal epithelium of 1-week-old chicks. Finally, we show that in chicks infected with serotype Typhimurium at 1 week of age, the level of fecal shedding of this organism does not reflect the level of cecal colonization as it does in murine models.ConclusionIn our study, we highlight important differences in systemic and intestinal colonization levels between chick and murine serotype Typhimurium infections, and provide evidence that suggests that the role of SPI-1 may not be the same during colonization of both animal models.
Highlights
IntroductionA major source of infection for humans is consumption of chicken or egg products that have been contaminated with Salmonella enterica serotype Typhimurium, our knowledge regarding colonization and persistence factors in the chicken is small
Salmonellosis is one of the most important bacterial food borne illnesses worldwide
We assayed the colonization of the liver in serotype Typhimurium-infected chicks, which followed the same pattern of colonization with very low numbers of organisms as the spleen in infected chicks
Summary
A major source of infection for humans is consumption of chicken or egg products that have been contaminated with Salmonella enterica serotype Typhimurium, our knowledge regarding colonization and persistence factors in the chicken is small. There are an estimated 1.4 million cases annually of food related illness caused by non-typhoidal Salmonella in the United States [1]. Serotype Typhimurium is the most prevalent serotype associated with food related illness in the United States [4,5,6], and consumption of contaminated poultry and egg products are often associated with clinical illness in humans [5]. In chicks over a few days of age, serotype Typhimurium colonizes the gastrointestinal tract but does not cause clinical disease [7]. Infected chicks are able to shed serotype Typhimurium into the environment for extended periods of time increasing the risk for environmental contamination, spread of the organism within the flock and contamination of the food supply
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