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To determine the effect of olestra on microbial ecology of the gut, faecal short-chain fatty acids (SCFAs) and water content were assessed in 93 subjects in a 36 d parallel, placebo-controlled, double-blind study. Faecal SCFAs and water content were determined at the end of an 8 d low fibre baseline period and 28 d treatment period. The test meal consisted of either a moderate (7 g) or high (24 g) level of fibre and olestra (24 g) or an equivalent amount of conventional fat. Olestra had a significant effect on both faecal water content and SCFAs. The water content decreased and concentrations of some SCFAs increased. The effect of olestra on SCFA concentrations in faeces (mmol/kg) differed with different fibre content of the meal. When the SCFAs were expressed as mmol/1 faecal water, a similar pattern of changes (several SCFAs increased) was observed for both olestra groups. Although all individual SCFA values were within the range of a healthy population, the effects were consistent, and potential reasons for it are discussed.

Faecal concentrations of short chain fatty acids (SCFAs) and faecal water content were determined in 93 healthy volunteers. We found positive correlation between faecal water content and the concentration of acetic, propionic and butyric acid. Multiple correlations between different SCFAs were found and grouping of the correlations according to an assumed substrate specificity was observed. Acetic, propionic and n-butyric acid, that are derived from carbohydrates, were best related to each other, whereas the minor acids, derived mostly from proteins, formed another group. Some specific features of the branched chain fatty acids (iso-acids) were discovered: their faecal concentrations were very strongly correlated to each other (Rho=0.977), they did not correlate with the total concentration of SCFAs, and showed negative correlations to the faecal water content. These findings suggest that the iso-acids have common and specific substrates in vivo, possibly of endogenous origin.

The jejunal, ileal and colonic microfloras were determined in 14 control rats and in six rats after a 5d course of metronidazole in high dose. Faecal short-chain fatty acids (SCFAs) were determined in 49 controls and in 14 treated rats. Metronidazole caused different changes in the microflora of different sites. In the jejunal lumen and on the mucosa the drug suppressed the numbers of lactobacilli and anaerobic cocci. In the ileal contents the levels of streptococci and lactobacilli increased and those of anaerobic cocci decreased, whereas no changes took place on the ileal mucosa. The microflora of colonic contents also remained unaffected but on the colonic mucosa the numbers of bacteroides decreased significantly. Metronidazole also caused significant changes in faecal SCFAs. The concentration of all acids decreased but the relative proportion of acetic acid increased (81 per cent versus 60 per cent in controls), obviously reflecting the suppression of anaerobic bacteria. It is concluded that metronidazole, given orally in high doses, has a significant effect upon the normal intestinal microflora that may not be reflected in faecal cultures. For evaluating an individual it seems to be useful to account for not only the absolute amounts of microbes but also their relative distribution and predominant/subordinate pattern in a particular site of the gastrointestinal tract.

To determine the effect of olestra on microbial ecology of the gut five microflora associated characteristics (MACs) were assessed in 93 subjects in a 36 d parallel, placebo-controlled, double-blind study. Degradation of tryptic activity, β-aspartylglycine and mucin, and conversion of cholesterol to coprostanol and bilirubin to urobilinogen were determined in faecal samples collected at the end of an 8 d low fibre baseline period and 28 d treatment period. The test meal consisted of either a moderate (7 g) or high (24 g) level of fibre and olestra (24 g) or an equivalent amount of conventional fat. Olestra had no effect on degradation of tryptic activity or β-aspartylglycine, and no consistent effect on mucin degradation. Olestra reduced significantly the conversion of cholesterol to coprostanol and urobilin to urobilinogen although the individual values were all within the range of healthy population after treatment. The lipophilic nature of cholesterol and urobilin is the most likely reason for the findings, as parts of the substrates partition into olestra and are not available to microorganisms.

Faecal short-chain fatty acids (SCFAs) were determined in children with shigellosis (n=22) or salmonellosis (n=11) prior to treatment and 5 d and 10 d after treatment with an antibacterial drug (TMP-SMX or Polymyxin, 5 d), or Lactobacillus GG (1010 - 1011 CFU/d, 10 d), or both had been started. At admission the SCFA concentrations were very low. Acetic, propionic and iso-valeric acid were significantly higher in shigellosis than in salmonellosis. The SCFA concentrations increased significantly during treatment, reaching those of adults by the 5th day and exceeding them by the 10th day, and showed no difference between the diseases after the 1st day. Adminsitration of Lactobacillus GG resulted in increased concentration of propionic acid by the 5th day of treatment and difference in iso-caproic acid in the 10th day samples: it was not found in any child who had received Lactobacillus GG but was present in half of the samples from the group treated solely with antibacterial drug. Iso-caproic acid is not found in healthy adults and may be indicative of Clostridium difficile. The disturbances in microbial ecology of the gut in enteric infections may have different characteristics depending on the aetiological agent. Treatment with Lactobacillus GG promotes recovery of the ecosystem as reflected by the faecal SCFAs.