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United States Department of Agriculture

Agricultural Research Service

2009 Annual Report

1a.Objectives (from AD-416)
(1) Investigate the molecular mechanisms that coordinate virulence and antibiotic resistance in Salmonella obtained from cattle (DT104 and S. dublin) and swine (DT104 and S. choleraesuis). (2) Characterize the molecular mechanisms involved in Salmonella survival, colonization and pathogenicity in relation to various host (swine and cattle) factors such as stress, gastric pH, and protozoa. (3) Investigate the molecular basis for swine resistance to Salmonella colonization by characterizing the immunological aspects of infection.

1b.Approach (from AD-416)
(1) Use a novel reporter system and transposon mutagenesis to identify DT104 genes involved in rumen protozoa-mediated hypervirulence. (2) Use an in vitro conjugation system to chracterize intra-protozoal transfer of plasmids from Klebsiella (and other bacteria) to Salmonella. (3) Compare the progression of salmonellosis for defaunated and fully-faunated calves infected with DT104. (4) Functional genomic analyses will be performed on Salmonella exposed to norepinephrine, low pH, and conditions relevant to intestinal colonization. (5) Use microarrays to identify swine genes that contribute to innate resistance to Salmonella colonization.

3.Progress Report
A gene important for survival of Salmonella in the pig has been identified by our laboratory. The predicted function of the bacterial gene product indicates that a mutation in the gene would result in different proteins being produced by the mutated Salmonella. Analysis of the proteins produced by the mutant Salmonella compared to wild-type Salmonella has identified differences in protein production that influence the in vivo and environmental survival of Salmonella. This investigation provides specific Salmonella genes to target for controlling the initial stages of Salmonella colonization and infection.

Isolates of multi-drug resistant Salmonella enterica serovar Typhimurium definitive phage type 104 (DT104) have been found worldwide in humans and in domestic livestock, such as cattle, poultry, and swine. DT104 strains usually encode 5 or more antibiotic resistance genes located in the Salmonella Genomic Island 1 (SGI-1), a 43-kb region that contains 44 open reading frames. Previous studies have identified that DT104 isolates containing SGI-1, when exposed to cattle rumen protozoa, become hyperinvasive/hypervirulent. We developed a real-time PCR assay to measure the transcriptional profile of these 44 genes, which can easily be expanded to test any other gene of interest in the genome. Our goal is to identify those genes in SGI-1 that are differentially regulated in DT104 in response to cattle rumen protozoa; these genes are believed to underlie virulence factors necessary to cause the hyperinvasive phenotype in S. Typhimurium DT104.

1. Salmonella-Infected Cows are an Animal Health and Food Safety Issue for the Cattle Industry. In our efforts to identify Salmonella control methods, we isolated a bovine-adapted, probiotic Escherichia coli strain capable of decreasing Salmonella viability in cattle. In cooperation with the National Cattlemen’s Beef Association, the E. coli strain possessing the bacteriocin-like activity was isolated from Salmonella-negative bovine feces from a herd with endemic Salmonella infection. Discovery of this native microbiota that reduces Salmonella in persistently infected cattle herds may offer economic advantages to cattle producers.

2. Salmonella-Carrier Pigs are a Serious Concern for Swine Health, Food Safety and Environmental Contamination. Scientists at the National Animal Disease Center in Ames, IA in cooperation with Iowa State University have classified porcine genes that are differentially expressed in pigs identified as low fecal shedders of Salmonella compared to high fecal shedders of Salmonella. These differentially expressed genes are establishing a gene expression “predictor” for identifying pigs that are more prone to shed Salmonella in their feces, thereby providing targets for biotherapeutics, diagnostic testing and the identification of Salmonella-resistant lines of pigs.

Review Publications
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.

Patton, T.G., Sharma, V.K., Carlson, S.A. 2009. Evaluation of the Control of Pathogen Load by an Anti-Salmonella Bacterium in a Herd of Cattle with Persistent Salmonella Infection. American Journal of Veterinary Research. 70(1):92-98.

Last Modified: 11/26/2015
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