Submitted to: Extension Publications
Publication Type: Experiment Station
Publication Acceptance Date: November 15, 2004
Publication Date: N/A
Technical Abstract: During stressful events such as transportation and mixing in swine, the release of various hormones (i.e., norepinephrine) increases. Related in vitro research has demonstrated that exposure of Salmonella to norepinephrine has dramatic affects on resulting bacterial virulence and population numbers. Our efforts sought to determine the relationship norepinephrine exposure to Salmonella would have on the infectious potential of the bacteria. To define this relationship, we exposed Salmonella enterica serovar Typhimurium to either in vitro NE or Luri Bertrani (LB) control culture conditions; resulting bacteria were then used to infect naïve nontransported animals (Experiment 1) or naïve animals that underwent a transportation/mixing scenario (Experiment 2). Animals were then sacrificed at 3 and 24 h post-infection whereupon a variety of tissues were collected and analyzed to determine the presence and quantity of bacteria in each. Our data suggest that the NE-exposed Salmonella manifest: 1) a greater capacity to associate with various tissues (most interestingly gastric epithelium), 2) an altered rate and route of tissue colonization, 3) an altered rate and concentration of Salmonella shed into the feces. Specifically, when animals were not transported (Experiment 1), in vitro norepineprhine exposure was found to increase the resulting bacterial concentration at 3 hours in the ileocecal lymph node and stomach wall tissues (p<.05). At the 24 hour time point, norepinephrine exposure increased bacteria concentrations in the ileocecal lymph node (p<.01), colon (p<.01), cecal contents (p<.01), and cecum (p<.05). At the 24 hour time point, all tissues with significant differences between treatments had greater bacterial concentrations in the norepinephrine exposed treatment compared to the LB treatment. In Experiment 2 where animals were transported and mixed immediately pre-infection, no differences were found between treatments at 3 hours. However, at 24 hours, treatment differences were found in the ileocecal lymph node (p<.02), colon (p<.01), ileocecal junction (p<.01), cecal contents (p<.01), and fecal contents (p<.01). In contrast to Experiment 1, all tissues affected by treatment were found to have greater bacteria concentrations in the LB treatment compared to the NEX treatment. Contemporary research has been unable to determine how and why bacteria outbreaks seem to occur during stressful periods, such as mixing and transportation. The current work offers evidence to explain how bacteria are able to manifest such rapid infectious capacities at times. Our results provide additional evidence to encourage the reduction of stress in all aspects of swine production, particularly during transportation and mixing.