Coliforms and generic E. coli are poor predictors of the behavior of human pathogens (like Salmonella, pathogenic E. coli and Listeria) in the crop production environment. Mounting evidence suggests that accurate models of Salmonella behavior in the production environment will have to be built based on the experiments conducted with Salmonella, and not based on data from distantly related surrogates like generic E. coli. This, however, necessitates availability and careful characterization of “disarmed” strains of Salmonella that could be used for on-site research. Upon completion of this study we will have developed robust tools for modeling behavior of these outbreak strains in the pre- and post-harvest production environments. The purpose of this project is to carry out comparative genomic and physiological characterization of the outbreak strains under production conditions and to compare them with the nonvirulent strain of Salmonella that we have developed. We will also have tested two key hypotheses aimed at understanding why only a dozen out of over 2,500 Salmonella serovars are associated with produce-linked outbreaks of illness. With previous CPS funding we engineered and verified the first nonvirulent, nontransgenic strain of Salmonella suitable for on-site studies as an indicator organism.