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This study was attempted to see more clear relationships among the enterobacteria, especially between the intestinal normal flora and pathogenic bacteria. It has been known that some intestinal normal flora produce the bacetrial metabolites that are harmful to other enteric bacteria. One of the metabolites is known as colicin, the protein fraction, which possesses certain degree of inhibitory effect against other bacterial growth fraction, which possesses certain degree of inhibitory effect against other bacterial growth. As a preliminary study for a colicin purification, the antagonistic effect of E, coli to groups of Salmonella and Shigella has been studied by means of in vitro quantitative culture method. 1. E.coli showed definite inhibitory effects against both Salmonella and Shigella groups in the mixture of two organisms. 2. The inhibitory effects of E.coli in the E.coli-Salmonella and the E.coli-Shigella mixture occurred from 4 hours incubation following the inoculation. 3. Even the complete inhibition of pathogenic enteric bacterial growth was noticed in the E.coli-Salmonella mixture at overnight incubation. 4. Among the diluted mixtures, 1:100, 1:1,000, and 1:10,000, survival rate of pathogenic enteric bacteria in the mixtures with E.coli showed least affected at the 1:1,000 dilution. 5. It was found that the antagonistic effect against groups of Salmonella-shigella was depending upon the groups of the genera.
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