Colonization resistance against Pseudomonas aeruginosa in gnotobiotic mice.

Gnotobiotic (GB) mice were colonized with various groups of intestinal bacteria to determine which members of the indigenous flora would exert colonization resistance against Pseudomonas aeruginosa. P. aeruginosa was cultured from the faeces at levels of 10(3)-10(4) cells/g in GB mice inoculated with either the combination of bacteroides and clostridia obtained from conventional (CV) mice or the combination of bacteroides, lactobacilli and clostridia obtained from limited flora mice. The combination of lactobacilli and clostridia from CV mice also did not eliminate P. aeruginosa from GB mice. However, P. aeruginosa was not detected in the faeces of GB mice by 14 days after inoculation with the combination of bacteroides, lactobacilli and clostridia obtained from CV mice. Thus, a complex indigenous flora consisting of bacteroides, lactobacilli and certain clostridia obtained from CV mice but not clostridia obtained from limited flora mice is required to exert complete colonization resistance against P. aeruginosa in GB mice.