Biomedical subjects

C Allison

Publications and source records attributed to C Allison.

46 records · Page 3Linked to original sources

PubMed1988

Effect of nitrate on methane production and fermentation by slurries of human faecal bacteria.

Most probable number counts showed that denitrifying species were the numerically predominant NO3- reducing bacteria in the faeces of five methanogenic individuals [about 10(10) bacteria (g dry wt faeces)-1]. In faecal slurries, however, denitrification was a relatively minor route of NO3- dissimilation, since only about 3% of the NO3- was converted to gaseous products, with NO3- being mainly reduced to NO2- and NH4+. When KNO2 was added to the slurries, denitrification became quantitatively more significant with approximately 23% of the NO2- being lost as gaseous products. The addition of KNO3 (10 mM) to slurries containing either starch or casein significantly decreased H2 and CH4 production. The effect of NO3- on methanogenesis was twofold: firstly, H2 accumulation decreased due to diversion of electrons towards NO3-/NO2- reduction, and as a result of H2 being used as an electron donor for NO3- reduction, resulting in the removal of the methanogenic substrate; secondly, there was direct inhibition of methane-producing bacteria by NO3- and NO2-. In starch-containing slurries, acetate: butyrate molar ratios were increased when NO3- was added but this effect was not observed when casein replaced starch. These results show that the ability of NO3-/NO2- to act as an electron sink can significantly influence the major products of the human colonic fermentation.

Bacteria↗

PubMed1988

Contribution of the microflora to proteolysis in the human large intestine.

Protease activities in human ileal effluent were approximately 20-fold greater than in normal faeces. Comparative studies with faeces from a person who did not have a pancreas suggested that a substantial proportion of the proteolytic activity in normal faeces was of bacterial origin. Thimerosal, iodoacetate, EDTA and cysteine significantly inhibited proteolysis in faeces, but not in small intestinal contents, showing that cysteine and metalloproteases were produced by bacteria in the large gut. These results, together with results from studies using p-nitroanilide substrates, demonstrated that faecal proteolysis was both qualitatively and quantitatively different from that in the small intestine. Studies with pure cultures of proteolytic gut bacteria indicated that the cell-bound proteases of Bacteroides fragilis-type organisms were likely to contribute significantly towards proteolytic activity associated with the washed cell fraction and washed particulate fraction of faeces. Extracellular proteases were formed by Streptococcus faecalis ST6, Propionibacterium acnes P6, Clostridium perfringens C16, Cl. bifermentans C21 and Cl. sporogenes C25. Inhibition results suggested that these bacteria, and similar organisms, may be partly responsible for the extracellular proteolytic activity found in the cell-free supernatant fraction of faeces.

Aminopeptidases↗

PubMed1986

Protein degradation by human intestinal bacteria.

Analysis of human gut contents showed that substantial quantities of soluble protein, ammonia and branched chain volatile fatty acids occurred throughout the large intestine [0.1-24.4 g (kg contents)-1, 7.7-66.0 mmol (kg contents)-1 and 1.5-11.1 mmol (kg contents)-1 respectively]. The presence of these metabolites suggested that substantial proteolysis was occurring. In vitro studies showed that casein and bovine serum albumin were partly degraded in slurries of human faeces over a 96 h incubation period, to produce TCA-soluble peptides, ammonia and volatile fatty acids. Proteolytic activity detected in the stools of five individuals ranged from 3.5 to 19.8 mg azocasein hydrolysed h-1 (g faecal material)-1. Washed cell and washed particulate faecal fractions accounted for 24-67% of total activity. The predominant proteolytic bacteria in the faecal samples examined were identified as Bacteroides spp. [1.0 X 10(11)-1.3 X 10(12) (g dry wt faeces)-1] and Propionibacterium spp. [1.2 X 10(8)-1.0 X 10(10) (g dry wt faeces)-1]. Other proteolytic bacteria which occurred in lesser numbers were identified as belonging to the genera Streptococcus, Clostridium, Bacillus and Staphylococcus. These results demonstrate that the gut microflora could potentially play a major role in proteolysis in the human colon.

Bacillus↗

PubMed1985