2008 Annual Report
Identified and characterized cells in the large intestines of cattle that have Shiga toxins (Stx) receptors (molecules that bind Stx). Identified Stx receptor-positive epithelial cells which were not responsive to Stx and novel Stx receptor-positive non-epithelial cells which were responsive to Stx. The identification of cells with varying Stx receptor expression patterns and Stx responsiveness will help elucidate the roles of different types of host cells during STEC colonization of the bovine intestine and determination of how Stx promote STEC persistence in cattle.
Constructed QseA and SdiA mutants of O157:H7 and are using them to test the hypothesis that O157:H7 mutants lacking the QseA mutant will not colonize and persist in cattle intestines as well as the SdiA mutant. Quorum sensing (QS) signaling molecules help bacteria coordinate their behavior based on bacterial densities in their environment. This research will help define the role QS molecules (produced by O157:H7, other intestinal bacteria, or bovine intestinal tissues) play in STEC colonization of cattle.
In vivo gene expression: Used a novel genetic selection procedure, along with bacteriophage-mediated transduction, to transfer specific mutations to wild type pathogenic E. coli strains which are normally resistant to this gene transfer system. The generalized procedure, which can be adapted to transfer any desired mutation to wild type E. coli, facilitates the construction of isogenic (i.e., differ only by desired mutation) mutants. We will use these mutants to identify nutritional requirements of E. coli within the intestinal tract.
Interventions: Evaluated a metabolic inhibitor of E. coli growth for use as a treatment of E. coli infections in animals. This inhibitor reduced the incidence of diarrhea and the numbers of bacteria in the intestines of neonatal pigs experimentally inoculated with pathogenic E. coli. The results provide evidence that this metabolic inhibitor may be useful for decreasing intestinal colonization and fecal shedding of E. coli in infected food animals.
Postweaning colibacillosis: Developed a simple, rapid multiplex PCR assay for simultaneous identification of 9 major virulence factors associated with postweaning colibacillosis (5 adhesins, 3 enterotoxins and Shiga toxin 2e). This simple, rapid, comprehensive test will facilitate diagnosis of colibacillosis and rapid characterization of pathogenic E. coli from swine. This project addresses National Program 108 Food Safety Action Plan Sections 1.1.1 Methodology, 1.1.3 Ecology, Host Pathogen, and Chemical Contaminants Relationships, and 1.1.4 Intervention Strategies.
1)calves treated with dexamethasone were more susceptible to STEC O157:H7 colonization;.
2)colon and cecum were sites from which inoculum type bacteria were most often recovered;.
3)rectum, ileo-cecal valve and distal colon were sites most likely to have O157-associated tissue damage;.
4)ileum and gall bladder were other sites with STEC O157:H7. Identification of sites where STEC O157:H7 initially colonize in experimentally inoculated weaned calves will facilitate identification of bacterial and host factors that promote STEC infections in cattle. Knowing where STEC O157:H7 initially colonize in cattle is critical for designing and evaluating strategies aimed at reducing STEC infections in cattle. This project addresses National Program 108 Food Safety Action Plan Sections 1.1.1 Methodology, 1.1.3 Ecology, Host Pathogen, and Chemical Contaminants Relationships, and 1.1.4 Intervention Strategies.
5.Significant Activities that Support Special Target Populations
Menge, C., Nystrom, E.A. 2008. Dexamethasone depletes gamma-delta T cells and alters the activation state and responsiveness of bovine peripheral blood lymphocyte subpopulations. Journal of Dairy Science. 91(6):2284-2298.
Sharma, V.K., Stanton, T.B. 2008. Characterization of a 3.3-kb plasmid of Escherichia coli O157:H7 and evaluation of stability of genetically engineered derivatives of this plasmid expressing green fluorescence. Veterinary Microbiology. Available: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TD6-4SKB3CT-2&_user=6956098&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000052423&_version=1&_urlVersion=0&_userid=6956098&md5=4acc7d9e43e9b59307dc8e59dc8022c6.