Comparison of cecal colonization of Salmonella enterica serotype Typhimurium in white leghorn chicks and Salmonella-resistant mice

Salmonellosis is one of the most important bacterial food borne illnesses worldwide. Among the many Salmonella serotypes, Typhimurium is the most commonly implicated serotype in human disease in the United States. A major source of infection for humans is consumption of chicken or egg products that have been contaminated with S. Typhimurium. The breadth of knowledge regarding colonization and persistence factors in the chicken is small when compared to our knowledge of factors that are important for these processes in other species used in Salmonella research, such as cattle and mice. Defining the factors important for these processes in the chick is the first step in decreasing the transmission of Salmonella between animal and human hosts. In this work, we developed a chicken model to identify and study intestinal colonization and persistence factors of Salmonella enterica serovar Typhimurium. We studied the degree of enteric and systemic colonization of wild type S. Typhimurium ATCC14028, one of the most widely studied Typhimurium isolates, in White Leghorn chicks and in Salmonella-resistant CBA/J mice during infection. Furthermore, we determined the distribution of wild type S. Typhimurium and a SPI-1 mutant (invA) during competitive infection in the cecum of 1-week-old chicks and 8-week-old mice. Cell associated, intracellular and luminal distributions of these strains in the cecum were analyzed as total counts in each compartment and also as a competitive index. Localization of S. Typhimurium ATCC14028 and the role of SPI-1 in colonization are well studied in murine models of infection, but comparative infection in chicks with the same strain has not been undertaken previously. We show that the cecal contents are the major site for recovery of S. Typhimurium in the cecum of 1-week-old chicks and Salmonella-resistant mice. We also show that while SPI-1 is important for successful infection in the murine model, it is important only for cell association in the cecum of 1-week-old chicks. Finally, we found that in chicks infected at 1 week of age, bacterial counts in the feces do not reflect those seen in the cecum as they do in mice.