Interactions between representative strains of four predominant resident bacteria of the human colon, , and , and strains of seven enteropathogens, serogroup non O1, , and , were examined in studies with an anaerobic continuous flow culture system and medium resembling the content of the mouse caecum (MCM). Potent unilateral antagonism attributable to synergic activities of the resident bacteria against the enteropathogens was evident.

The four resident bacteria persisted at levels of 10 cfu/ml or more in single and in any mixed cultures of the resident species. The seven enteropathogens also persisted in single cultures. In contrast, was excluded in several days in mixed cultures with each of the four resident bacteria. and were excluded in the presence of alone. and serogroup non O1 were excluded in the presence of with and, in some cases, with additional species. was the most resistant; only 10-fold reduction of the population level was observed in mixed culture with all four of the resident species. When the amounts of some components in the medium, such as peptone and yeast extract, were increased, grew and persisted even in the presence of the four resident bacteria. , in contrast decreased steadily, even in enriched media.


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