Potent antagonism of Escherichia coli, Bacteroides ovatus, Fusobacterium varium, and Enterococcus faecalis, alone or in combination, for enteropathogens in anaerobic continuous flow cultures.
Interactions between representative strains of four predominant resident bacteria of the human colon, Escherichia coli, Enterococcus faecalis, Bacteroides ovatus, and Fusobacterium varium, and strains of seven enteropathogens, Yersinia enterocolitica, Shigella flexneri, Salmonella typhimurium, Vibrio parahaemolyticus, V. cholerae serogroup non O1, Staphylococcus aureus, and Clostridium perfringens, 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 c. 10(6) 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, Y. enterocolitica was excluded in several days in mixed cultures with each of the four resident bacteria. Sh. Flexneri and Staph. aureus were excluded in the presence of E. coli alone. C. perfringens, V. parahaemolyticus and V. cholerae serogroup non O1 were excluded in the presence of E. coli with B. ovatus and, in some cases, with additional species. S. typhimurium was the most resistant; only c. 10(2)-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, C. perfringens grew and persisted even in the presence of the four resident bacteria. Sh. flexneri, in contrast decreased steadily, even in enriched media.