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