Influence of Escherichia coli on Streptococcus faecalis in mixed cultures and experimental animal infections.

Strains of Escherichia coli (four strains) and Streptococcus faecalis (three strains) randomly isolated from faecal samples were cultured together in vitro and in experimental animal infections in order to evaluate the interaction of these two species. Streptococcus faecalis was eliminated from mixed cultures and infections at population ratios of Escherichia coli to Streptococcus faecalis of 10-100:1. The mechanism involved was probably an antibiotic substance produced by Escherichia coli which was antagonistic to Streptococcus faecalis. The substance appeared to be diffusible, water-soluble, of low molecular weight and insensitive to the protease trypsin. It was produced and remained active in vitro and in vivo and can probably be classified as a microcin.