Generation of Ammonia from Non-Urea Sources in a Faecal Incubation System

Abstract

1. A 25% faecal suspension in sodium chloride solution, incubated anaerobically at 37 degrees C for 48 h, showed excellent survival of all the main groups of faecal bacteria. 2. All faecal incubation systems studied generated large amounts of ammonia, particularly those in which bacterial counts fell during incubation. As normal faeces contain negligible amounts of urea this ammonia must have been generated from sources other than urea. 3. Ammonia was also generated by faeces delivered by sodium chloride enema, and by ileostomy fluid, indicating that the phenomenon is not confined to distal colonic contents. 4. Ammonia generation by incubated faeces was inhibited by prior autoclaving of the sample, but not by sterilization with gamma-irradiation. 5. Generation of ammonia by incubated stool was accompanied by release of large amounts of organic anion and a fall in pH. 6. These observations are interpreted as evidence that ammonia generated within the colon in situ is not derived exclusively from urea, but also from bacterial deamination of amino acids, peptides and proteins. Simultaneously bacterial activity generates large amounts of organacid. The presence of living bacteria is not essential for ammonia generation, provided that bacterial enzymes are present. 7. Bacterial generation of organic solute in faeces which have left the body is sufficiently rapid to cast serious doubts on the validity of faecal centrifugation, or other time-consuming techniques involving lengthy handling of faeces, as methods of obtaining extracellular faecal fluid for measurements of organic constituents or ammonia.

Role of pH in production of hydrogen from carbohydrates by colonic bacterial flora. Studies in vivo and in vitro.

“…In vitro incubation systems have been previously validated for the modeling of bacterial metabolism in the rumen (18) and in the human colon (19). Despite inherent limitations such as lack of bicarbonate secretion and absorption of organic acids which occur in vivo, short-term (1 h) incubations as used in the present studies have been shown to reflect accurately the rate of in vivo fermentation reactions (18,20).…”

Protein Degradation by Human Intestinal Bacteria

“…1). Vince et al (1976) showed that bacterial populations in faecal slurries remain substantially unchanged after incubation for 48 h at 37 "C. In order to remove readily utilizable substrates, faecal slurries in the present study were preincubated for 48 h before addition of casein or BSA. The rapid hydrolysis of protein, and the formation of metabolic end products in these slurries, confirmed that gut bacteria can survive and remain metabolically active for extended periods in vitro.…”

Ammonia production by intestinal bacteria: the effects of lactose, lactulose and glucose

“…These were isolated as described previously, mainly from the faeces of healthy adult subjects, but some isolates from the terminal ileum were also examined (Hamilton et al, 1970;Vince et al, 1976). Numerically dominant groups of bacteria were selected for testing, and placed in one of the following categories, account being taken of several criteria including, the ability to grow aerobically or anaerobically, gram-staining properties and spore formation: enterobacteria; streptococci; micrococci; Bacillus spp.…”