Abstract
The adequacy of a human faecal microbiota associated mouse as a model for studying the activities of human intestinal microorganisms was examined. During a 6 month period, several predominant aerobic and anaerobic components of the human faecal bacteria persisted at stable numbers 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 presence of short-chain fatty acids and non-fatty organic acids in the caeca of the associated mice. The relative concentrations of the two acid groups changed over a 21 d period, suggesting an alteration in the pattern of metabolism by the bacteria during the course of the study. The total amount of organic acid produced by the microorganisms in the caeca of the associated mice was approximately 25 per cent of the published value for humans, suggesting that the human microbiota retained only a portion of its metabolic activities in the mouse host. When challenged 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 study the ecology of the human intestinal tract. The disappearances of Bacillus and both aerobic and anaerobic Lactobacillus species may influence the outcomes of the studies. Moreover, the greatly reduced metabolic activity of the human faecal microbiota in the mouse may diminish the significance of the results of metabolic studies when extrapolated to the human situation. However, the model might have utility in studies on colonisation resistance against various enteric pathogens.