The invention includes compositions for treating an animal to inhibit the incidence and growth of E. coli O157:H7 and other pathogenic bacteria. The composition is a therapeutically effective amount of a Lactobacillus bacterium, or one, or a combination of a number of other probiotic bacteria. An alternative composition is a therapeutically effective amount of a lactic acid producing bacterium such as Lactobacillus bacterium in combination with a lactate utilizing bacterium such as Propionibacterium. One example of the Lactobacillus bacterium is Lactobacillus acidophilus, and one example of the Propionibacterium is Propionibacterium freudenreichii.