Summary auto-generated
This study investigated how 64 strains of colonic bacteria ferment lactulose, a synthetic disaccharide used clinically for treating constipation and hepatic encephalopathy. Bacteria were cultured anaerobically in lactulose-containing media, and their fermentation products were quantified. Results showed significant variation in lactulose utilization among bacterial species: some organisms could not metabolize it, while clostridia and lactobacilli fermented it extensively. The major non-gaseous fermentation products were acetic, lactic, and butyric acids, with only hydrogen and carbon dioxide detected as gases. Time-course experiments tracked product formation throughout bacterial growth cycles. Fermentation patterns from pure cultures correlated well with results from mixed faecal cultures, though pH conditions influenced product distribution. Under low pH conditions mimicking therapeutic lactulose dosing, acid-tolerant organisms predominated, generating mainly acetic, butyric, and lactic acids. These findings clarify the complex microbial metabolism of lactulose in the colon and provide insights into its therapeutic mechanisms.
Key findings
- Among 64 bacterial strains tested, 61% fermented intermediate amounts (5-20%) of lactulose, while 14% showed negligible utilization; lactobacilli and clostridia exhibited the highest fermentation rates
- Major fermentation products were acetic, lactic, and butyric acids; carbon dioxide and hydrogen were the only gases produced; formic acid was not detected
- Bacteroides predominantly produced acetic and succinic acids, while clostridia characteristically produced butyric acid and lactobacilli showed homolactic fermentation patterns
- Fermentation product profiles from mixed faecal cultures matched those of pure cultures, but pH maintenance above 5.5 shifted the product balance toward succinic and longer-chain fatty acids by favoring acid-sensitive organisms
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Abstract
SUMMARY: Sixty-four strains of intestinal bacteria were cultured under anaerobic conditions in lactulose-containing media to assess their ability to ferment lactulose. Some organisms were unable to metabolize the disaccharide, while others, e.g. clostridia and lactobacilli, metabolized lactulose extensively. Quantitative analyses of the fermentation products indicated that the major non-gaseous metabolites were acetic, lactic and butyric acids. Hydrogen and carbon dioxide were the only gases detected. Fermentation products were estimated for selected species throughout their growth cycles. The products of fermentation of lactulose by stool cultures varied with incubation conditions such as pH, but correlated well with those produced by pure cultures. These results are discussed in relation to the therapeutic uses of lactulose.