ADEQUACY OF THE HUMAN FECAL MICROBIOTA ASSOCIATED MOUSE AS A MODEL FOR STUDYING THE ECOLOGY OF THE HUMAN INTESTINAL-TRACT

The adequacy of a human faecal microbiota associated mouse as a model for studying the activities of human intestinal microorganisms was exa mined. During a 6 month period, several predominant aerobic and anaero bic components of the human faecal bacteria persisted at stable number s in the intestinal tracts of the mice. However, Bacillus species and both aerobic and anaerobic Lactobacillus species disappeared within 7 d after association. An inverse relationship existed between the prese nce of short-chain fatty acids and non-fatty organic acids in the caec a of the associated mice. The relative concentrations of the two acid groups changed over a 21 d period, suggesting an alteration in the pat tern of metabolism by the bacteria during the course of the study. The total amount of organic acid produced by the microorganisms in the ca eca of the associated mice was approximately 25 per cent of the publis hed value for humans, suggesting that the human microbiota retained on ly a portion of its metabolic activities in the mouse host. When chall enged orogastrically with Salmonella typhimurium, associated mice were as resistant to colonisation as conventional mice, but germfree mice were very susceptible. The results raise questions about the adequacy of the human faecal microorganisms associated mouse as a model to stud y the ecology of the human intestinal tract. The disappearances of Bac illus and both aerobic and anaerobic Lactobacillus species may influen ce the outcomes of the studies. Moreover, the greatly reduced metaboli c activity of the human faecal microbiota in the mouse may diminish th e significance of the results of metabolic studies when extrapolated t o the human situation. However, the model might have utility in studie s on colonisation resistance against Various enteric pathogens.