Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2008
Publication Date: 3/20/2009
Citation: Uthe, J.J., Wang, Y.F., Long, Q., Nettleton, D., Tuggle, C.K., Bearson, S.M. 2009. Correlating Blood Immune Parameters and a CCT7 Genetic Variant with the Shedding of Salmonella enterica Serovar Typhimurium in Swine. Veterinary Microbiology. 135(3-4):384-388. Interpretive Summary: Pigs that shed Salmonella in their feces are an animal health issue, a food safety problem and an environmental contamination risk. Our research program investigates the undesirable carrier state of Salmonella in pigs in order to identify approaches to control both clinical and sub-clinical (carrier) infections. The current research study compared various immune parameters in Salmonella-infected pigs with fecal shedding of the pathogen. The amount of a specific immune compound (interferon-gamma) in the blood of the infected pigs was higher in pigs shedding greater levels of Salmonella. Also, the higher the interferon-gamma levels in the blood, the greater the number of specific immune cells in the blood that fight infection. Furthermore, when we investigated the sequence of a specific porcine gene involved in Salmonella infections, we found that pigs with a certain DNA sequence were less likely to shed Salmonella in their feces than pigs with a different DNA sequence. Thus, pigs with this specific DNA sequence may be more resistant to infection with Salmonella. Our research has identified potential markers for Salmonella shedding. Specifically, the higher the levels of interferon-gamma in the blood of Salmonella infected pigs, the higher the levels of Salmonella shed in their feces. Additionally, differences in DNA sequence for a specific porcine gene was shown to associate with Salmonella shedding levels in swine. Industry, university and government researchers investigating Salmonella in swine should find this research interesting since identifying factors in the pig that control the ability of the animal to combat disease will uncover markers for classifying potential carrier pigs as well as targets for disease diagnosis, intervention and prevention.
Technical Abstract: In the current study, 40 crossbred pigs were intranasally inoculated with Salmonella enterica serovar Typhimurium and monitored for Salmonella fecal shedding and blood immune parameters at 2, 7, 14 and 20 days post-inoculation (dpi). Using a multivariate permutation test, a positive correlation was observed between S. Typhimurium shedding and interferon-gamma (IFNG) levels at 2 and 7 dpi (p<0.05), with a greater number of Salmonella shedding in the animals with higher IFNG levels. In addition, a positive correlation was observed between IFNG levels and the number of circulating neutrophils at 7 and 14 dpi, mature banded neutrophils at 2 dpi, monocytes at 7 dpi and white blood cells (WBCs) at 7, 14 and 20 dpi. We have further performed association studies of these immune response parameters as well as shedding status of the Salmonella-infected pigs with a single nucleotide polymorphism (SNP) identified in a porcine gene previously shown by our group to be transcriptionally regulated in swine experimentally inoculated with S. Typhimurium. Our analyses with the 40 pigs suggest a positive association (p<0.05) of SNP genotype A/G at nucleotide 1026 (relative to start codon) of the CCT7 gene with circulating neutrophils and WBCs and with Salmonella shedding at 7 dpi compared to the G/G heterozygote genotype. Linking specific genes and genetic polymorphisms with the porcine immune response to Salmonella infection and shedding may identify potential markers for carrier pigs as well as targets for disease diagnosis, intervention and prevention.