Short-chain fatty acids in intestinal content of germfree mice monocontaminated with Escherichia coli or Clostridium difficile.

The short-chain fatty acids (SCFAs) have been analysed in coecal and small-intestinal content of conventional (CONV) and germfree (GF) mice, in germfree mice monocontaminated with Escherichia coli (MEC) or Clostridium difficile (MCD), and in germfree mice conventionalized by the visitor technique (EXG). The total concentrations of SCFAs in coecal content, measured by gas chromatography, were (mean (SD), mmol/kg): CONV, 125.2 (32.9); GF, 1.02 (0.39); MEC, 6.88 (0.76); MCD, 4.50 (0.12); and EXG, 115.6 (17.4). The concentrations of SCFAs were 3- to 25-fold higher in the coecum than in the small intestine in CONV, MEC, and EXG mice (p less than 0.05). The fermentation patterns (that is, the relative composition of the acids) of E. coli and Cl. difficile were distinctively different under defined in vitro conditions and similar to those found in intestinal content of monocontaminated animals. Combined gas chromatography and mass spectrometry showed that Cl. difficile produced an unusual metabolite, 2-methylbutyric acid, in vitro and in vivo. The findings indicate that the fermentation patterns are closely related to the bacteria. Variations in the bacterial flora may be more important in determining the concentrations and patterns of SCFAs in intestinal content than variations in the intake of substrate for SCFAs formation as dietary fibre.