Escherichia coli O157:H7 is a foodborne pathogen that causes a variety of symptoms, from bloody diarrhea to hemolytic uremic syndrome. Previous research has shown that non-pathogenic strains of E. coli can affect the course of an E. coli O157:H7 infection. The objective was to identify the frequency in which non-pathogenic E. coli amplify Stx production. 100 human fecal isolates from the E. coli Reference Center were tested for increased levels of Stx production.