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Abstract
The survival of two colicine-sensitive strains of Escherichia coli when grown in mixed culture with each of three colicine-producing strains was investigated. The universal colicine indicator strain, E. coli B/TKM, was completely eliminated during mixed culture with each of the colicinogenic strains, whereas colicine-resistant mutants of it showed normal growth. The second colicine-sensitive strain, E. coli no. C600/21, was also eliminated by the colicine-B-producing strain, but not by either the colicine-E2- or E3-producing strains. The bacteria that were refractory to colicine E2 or E3 remained viable even in high concentrations of the colicine yet were unable to multiply; they regained full colicine sensitivity after growth in peptone water or when subcultured with a non-colicine producing strain of E. coli, but not when grown with a strain producing the same colicine. The refractory cells were non-colicinogenic and free colicine was present in the supernatant fluids of the mixed cultures. After treatment with trypsin to destroy the absorbed colicine the refractory cells regained their colicine sensitivity.
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