Competitive exclusion of intestinal colonization of Escherichia coli in chicks.

A native gut microflora of chickens that protected chicks against Salmonella was evaluated against six pathogenic strains of Escherichia coli using similar methodology. Nalidixic-acid-resistant forms of the E. coli strains were derived for use in seeder-bird and individual-bird challenge tests. A substantial degree of exclusion of intestinal colonization of each of the six pathogenic strains of E. coli was secured in chicks that had been treated with native gut microflora. E. coli appeared to colonize chiefly the crop and cecum. Native gut microflora limited to a much lesser degree the "normal" E. coli present in the intestinal tract of test chicks. The mechanism of protection appears to be similar to that for Salmonella: native gut microflora and E. coli competed for sites of attachment.