Shiga toxin-producing Escherichia coli (STEC) is one of the leading causes and accounts for a large economic burden due to foodborne illness in the U.S. Cattle and other ruminants serve as a reservoir for these organisms. In addition to the burden of STEC illness in humans, there is a tremendous economic loss to the beef industry associated with a recall due to STEC contamination. Thus, an intervention that reduces STEC contamination of food, and human foodborne illness is a major priority. Despite the recognition of the clinical significance of non-O157 STEC, along with the prototype STEC O157:H7, there is a lack of information on their collective virulence and persistence. A complete understanding of the virulence mechanisms of major STEC serotypes (O157 and non-O157) involved in outbreaks is required to develop these interventions and preventative measures against infections and contamination.We propose to use proteomic and targeted-mutagenesis approaches to advance the understanding of the mechanism of virulence of zoonotic STEC serogroups (O157 and non-O157) by evaluating bacterial surface proteins involved in colonization of human and cattle intestines. The goal of identifying surface proteins involved in persistence and virulence will fill the existing gaps in our knowledge regarding STEC infections and transmission. Our specific research objectives are: 1) Characterization of in vitro, ex vivo, and in vivo expressed STEC surface proteins during bacterial interaction with a human intestinal epithelial cell line (Caco-2 cells), cattle colonic explants, and in vivo in rabbit infection; and 2) Evaluate STEC surface proteins for adherence and virulence using clustered regularly interspaced short palindromic repeats technology to knockout genes corresponding to surface proteins expressed in STECstrains. Identification of proteins important for intestinal colonization and virulence will facilitate design of future vaccines against STEC infections and persistence in cattle. Reduction of STEC in cattle will improve food safety and increase the profitability and sustainability of the beef industry.