Some factors influencing colicin activity between pathogenic and commensal Escherichia coli from the pig.

Commensal strains of Escherichia coli derived from pigs had a broad spectrum of in vitro colicin acitivity against pathogenic serotypes. Of eight pathogenic serotypes tested, only three were colicinogenic and were active against relatively few commensal strains. Colicin activity was influenced by temperature, pH and oxygen tension as well as by the availability of certain nutrients and the presence of trypsin. Lack of colicin activity in intestinal supernatant fluid was ascribed to the concentration of trypsin present. It was concluded that colicins are unlikely to influence the dominance of pathogenic Escherichia coli serotypes in the pig's intestine, except possibly in the colon and rectum where the concentration of trypsin is low.