Studies on Amine Production in the Human Colon: Enumeration of Amine forming Bacteria and Physiological Effects of Carbohydrate and pH

High levels of amines were present in large intestinal material taken from five persons who had died suddenly. Mean total concentrations of simple aliphatic amines were approximately 22 mmol/kg in the proximal colon and 16 mmol/kg in the distal bowel, with propylamine, piperidine and methylamine predominating in all regions. Amine concentrations in faeces from six healthy donors ranged from 1·8 to 41·5 mmol/kg (mean 13·3, S.E.M. 5·9). A wide range of these metabolites was found in intestinal contents, of which trimethylamine and propylamine were quantitatively most important. Although considerable inter-individual variation was seen in faecal amine excretion, methylamine and dimethylamine were never detected in fresh faeces, indicating these substances were rapidly absorbed from the rectum. Net production rates of different amines in faecal material incubatedin vitrovaried from approximately 0·01 μmol/h/g for methylamine, cadaverine, histamine and tryptamine, to 1·26 μmol/h/g in the case of propylamine. Amines were further metabolised by colonic bacteria, especially in the presence of a fermentable carbohydrate source. Amine formation by faecal bacteria was maximal at near neutral pH, while culture in the presence of a fermentable carbohydrate source reduced net amine production by 80%.Confirmatory evidence for the importance of pH and carbohydrate availability on amine production was obtained in experiments with 16 pure cultures of intestinal bacteria. Most probable number (MPN) counts of amine producing bacteria in faeces from four healthy donors showed that high numbers of methylamine, dimethylamine and propylamine forming bacteria were present in every sample. However, considerable variability was seen in carriage rates of bacteria forming other amines, especially with respect to histamine, butylamine and phenylethylamine. Measurements of individual amine concentrations in MPN tubes showed that propylamine constituted about 70% of total amine production at all sample dilutions, and that while high populations of histamine forming bacteria were present in faecal samples, very small amounts of this product were formed.