Submitted to: Safepork
Publication Type: Proceedings
Publication Acceptance Date: May 7, 2007
Publication Date: May 11, 2007
Citation: Bearson, B.L., Bearson, S.M. 2007. The QseBC Quorum Sensing System is Involved in Salmonella enterica serovar Typhimurium Colonization of the Swine Gastrointestinal Tract. In: Proceedings of the 7th International Symposium on the Epidemiology and Control of Foodborne Pathogens in Pork, May 9-11, 2007, Verona, Italy. p. 409-412.
The response of bacteria to hormone-like, chemical molecules is termed quorum sensing, a mechanism for cell-to-cell communication that includes sensing the host environment. In the gastrointestinal tract, at least two quorum sensing molecules are present that activate the bacterial QseBC quorum sensing system, autoinducer-3 (AI-3) and norepinephrine (NE). AI-3 is produced by bacteria, whereas NE is produced by the host, often during stress. We have demonstrated that the motility of Salmonella enterica serovar Typhimurium is enhanced in the presence of NE and 10% pre-conditioned medium (AI-3) from the wild-type strain. Additionally, DNA microarray and qRT-PCR analyses revealed transcriptional induction of motility genes in the presence of NE. The enhanced motility of S. Typhimurium to both NE and AI-3 requires the qseC gene, encoding the QseC sensor kinase. To determine whether the QseBC quorum sensing system is involved in colonization of the swine gastrointestinal tract, a competitive index (CI) experiment was performed. Swine were intranasally inoculated with a 1:1 ratio of a qseC mutant and the wild-type strain. At 1, 2 and 3 days post-inoculation (d.p.i.), fecal samples were obtained for quantitative bacterial culturing. The mean CI of the qseC mutant to the wild-type strain (n=6) was 0.13, 0.08, and 0.03 at 1, 2 and 3 d.p.i., respectively (p<0.01). At 7 d.p.i., necropsies were performed and tissue samples obtained for quantitative bacterial cultures. The mean CI of the qseC mutant/wild-type strain for cecum and tonsil tissues at day 7 were 0.02 and 0.4, respectively (p<0.01). Significant differences in the presence of the qseC mutant to the wild-type Salmonella were also observed for the ileal Peyer’s Patches, ileocecal lymph nodes and fecal samples. This research demonstrates that the QseBC system of S. Typhimurium responds to NE/AI-3, and the QseBC system is important for colonization of the swine gastrointestinal tract and porcine tissues.