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

Transporting swine to slaughter is often linked with an increase in shedding of Salmonella, but little information exists to explain the role of stress. Recent research has suggested the catecholamine norepinephrine (NE) as a potential host signal during stress. The current study sought to investigate the prevalence of Salmonella enterica serovar Typhimurium in fecal samples and various tissues following inoculation with S. Typhimurium exposed to NE in vitro. The samples were collected at 3 and 24 h post-inoculation (p.i.) from pigs inoculated with S. Typhimurium cultured in either Luria–Bertani medium (LBC) or NE-infused, SAPI minimal medium (NEC). Bacterial quantification of tissue and fecal samples revealed a difference in the concentration of Salmonella between the two infections for six tissues at the two time points, five of which were greater in the NEC animals (p<0.05). Upon observing an increase in the number of Salmonella associated with the stomach wall tissues at 3 h p.i. for the NEC culture, an experiment was conducted using an ex vivo swine contents assay to determine the effect of NE exposure on the ability of the organism to survive the conditions of the porcine stomach; NE treatment enhanced the survival of S. Typhimurium more than 2 logs (p<0.007). Our results demonstrate an increase in the number of Salmonella associated with various swine tissues following experimental inoculation with NE-treated S. Typhimurium; thus, a possible scenario could be envisioned with a Salmonella-infected pig being stressed during transportation/mixing, resulting in the shedding of NE-stimulated Salmonella and exposure of naïve, stress-compromised penmates with a “primed” microorganism.