Cultivation of Salmonella enterica serovar Typhimurium in a norepinephrine-containing medium alters in vivo tissue prevalence in swine

Authors: Toscano, Michael; Stabel, Thomas; Bearson, Shawn; Bearson, Bradley - Brad; Lay Jr, Donald

Submitted to: Journal of Experimental Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2006
Publication Date: 2/15/2007
Citation: Toscano, M.J., Stabel, T.J., Bearson, S.M., Bearson, B.L., Lay Jr, D.C. 2007. Cultivation of Salmonella enterica serovar Typhimurium in a norepinephrine-containing medium alters in vivo tissue prevalence in swine. Journal of Experimental Animal Science. 43(4):329-338.

Interpretive Summary: Salmonella outbreaks during transportation and mixing of swine are a tremendous financial burden on the livestock industry due to reduced weight gain, veterinary treatment, and other factors. Despite the widespread problems caused by Salmonella, the mechanisms associated with these outbreaks remain elusive. Recent in vitro work in microbiology has found that norepineprhine, a hormone well associated with the stress response, has potent effects on the growth and virulence of gram negative bacteria, including Salmonella. The current work sought to develop an in vivo model of this relationship by inoculating Salmonella that were exposed to in vitro norepinephrine onto Salmonella-free pigs. A second procedure compared the survivability of bacteria exposed to NE and not exposed to NE when incubated in ex vivo stomach contents. Our results from the first procedure found that norepinephrine increased the concentration of bacteria in the majority of tissues suggesting an enhanced infectious ability, possibly by expediting key life processes. Results from the second procedure found norepinephrine exposure enhances survivability in the acidic conditions of the stomach. In conclusion, the current study supports that norepinephrine exposure affects resulting concentrations in the host, possibly by expediting key processes and enabling the bacteria to overcome host defenses such as stomach acidity. The impact of these results will allow producers to better understand the spread of infectious bacteria in swine during stressful events, such as transportation.

Technical Abstract: Salmonella outbreaks, commonly associated with transportation and mixing, are a tremendous burden to the swine industry due to increased veterinary costs and reduced weight gain. Despite these losses, little is known in regards to why Salmonella outbreaks occur during such critical periods. A well-established response has been shown within microbiology literature that in vitro exposure to norepinephrine, a hormone that manifests dramatic increases during stressful events, has potent effects on resulting bacteria concentrations. The objective of the current study was to determine what effect in vitro norepinephrine exposure would have on resulting infectious capacity of bacteria in a live animal. For this purpose, Salmonella inoculum was cultivated in vitro in either a norepinephrine-infused (NEC) or standard Luri-Bertrani (LBC) broth and then used to infect Salmonella-free animals. Animals were sacrificed at 3 and 24 hours post-infection. The tissue and fecal samples were collected and bacterial concentrations were quantified. A second ex vivo experiment was added to determine the effect of NE exposure on the bacteria’s ability to survive conditions of the stomach, i.e. low pH. In vitro norepinephrine exposure was found to increase the resulting bacterial concentration of NEC animals at 3 hours in stomach wall tissues (p<.05) while the LBC treatment induced a greater bacterial concentration in the ileo-cecal lymph node (p<.05) and colon (p<.08). At the 24 hour time point, norepinephrine exposure increased bacteria concentrations in the ileo-cecal 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 NEC treatment compared to the LBC treatment. Lastly, the ex vivo stomach assay found that NE-exposed bacteria were better able to survive stomach contents. Our results suggest that NE exposure of bacteria enhances Salmonella’s infectious capacity, possibly by expediting key processes and enabling acid adaptive mechanisms. Such a relationship between NE exposure and infectious capacity may provide the bacteria a means to exploit a stress-induced, immune compromised animal and increase the likelihood of infection.