Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/15/2011
Publication Date: 12/12/2011
Citation: Huang, T., Uthe, J.J., Bearson, S.M., Demirkale, C.Y., Nettleton, D., Knetter, S.M., Christian, C.M., Ramer-Tait, A.E., Wannemuehler, M.J., Tuggle, C.K. 2011. Distinct peripheral blood RNA responses to Salmonella in pigs differing in Salmonella shedding levels: intersection of IFNG, TLR and miRNA pathways. PLoS One [serial online]. 6(12). Available: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028768. Interpretive Summary: On the farm as well as in experimental infections, the level of Salmonella colonization, carriage and shedding in pigs varies greatly. Genetics of the pig is likely to play an important role in this differential response to Salmonella; thus, the use of genomics to identify pigs that are naturally more resistant to Salmonella is a promising method to address food safety by selecting favorable pigs to breed for Salmonella-resistant offspring. This study compared the expression of genes in pigs classified as low versus persistent Salmonella shedders. At 2 days following inoculation with Salmonella enterica serovar Typhimurium, differences in gene expression of key porcine regulatory systems were observed between the two shedding classes.Of particular interest is the decreased expression of the regulatory microRNA (miR-155) only in the pigs that persistently shed Salmonella. Information about porcine genes and genetic pathways that influence swine resistance to Salmonella will support the development of a classification tool that recognizes the desirable low Salmonella shedder phenotype on farms, thereby advancing selective breeding programs for Salmonella-resistant pigs. Swine producers and researchers at university, industry and government institutions that are interested in selection of livestock naturally resistant to foodborne pathogens (genetic improvement) as an approach to reduce antibiotic usage on the farm and enhance food safety will find interest in this research.
Technical Abstract: Transcriptomic analysis of the response to bacterial pathogens has been reported for several species, yet few studies have investigated the transcriptional differences in whole blood in subjects that differ in their disease response phenotypes. Salmonella species infect many vertebrate species, and pigs colonized with Salmonella enterica serovar Typhimurium (ST) are usually asymptomatic,making detection of these Salmonella-carrier pigs difficult. The variable fecal shedding of Salmonella is an important cause of foodborne illness and zoonotic disease. To investigate gene pathways and biomarkers associated with the variance in Salmonella shedding following experimental inoculation, we initiated the first analysis of the whole blood transcriptional response induced by Salmonella. A population of pigs (n=40) was inoculated with ST and peripheral blood and fecal Salmonella counts were collected between 2 and 20 days post-inoculation (dpi). Two groups of pigs with either low shedding (LS) or persistent shedding (PS) phenotypes were identified. Global transcriptional changes in response to ST inoculation were identified by Affymetrix Genechip® analysis of peripheral blood RNA at day 0 and 2 dpi. ST inoculation triggered substantial gene expression changes in the pigs and there was differential expression of many genes between LS and PS pigs. Analysis of the differential profiles of gene expression within and between PS and LS phenotypic classes identified distinct regulatory pathways mediated by IFN-gamma, TNF, NFkB, or one of several miRNAs. We confirmed the activation of two regulatory factors, SPI1 and CEBPB, and demonstrated that expression of miR-155 was decreased specifically in the PS animals. These data provide insight into specific pathways associated with extremes in Salmonella fecal shedding that can be targeted for further exploration on why some animals develop a carrier state. This knowledge can also be used to develop rational manipulations of genetics, pharmaceuticals, nutrition or husbandry methods to decrease Salmonella colonization, shedding and spread.