The effect of lactulose on DNA damage induced by DMH in the colon of human flora-associated rats.

Germ-free rats were fed purified diets containing sucrose (0.3%, wt/wt) as control or the synthetic disaccharide lactulose (0.3% wt/wt) and were then dosed orally with a human fecal suspension.

Continuous culture of human faecal bacteria as an in vitro model for the colonic microflora.

To investigate the role of human gut bacteria in the metabolism of potentially reactive compounds we have developed an in vitro model of the human faecal microflora using a two-stage continuous culture inoculated with human faeces. The cultured bacterial population retained many of the bacteriological and biochemical characteristics of the flora present in the faecal sample used for inoculation. Obligate anaerobes were the predominant bacterial types found in vitro and included Bacteroides ovatus and Bifidobacterium adolescentis.

Modified mutagen activation in hepatic fractions from rats fed dietary rutin--interaction between gut flora and host metabolism.

Male Sprague-Dawley rats were fed a purified diet or one supplemented with the glycosidic plant flavonoid (+)rutin for 14 days. Rutin treatment significantly increased caecal bacterial beta-glucosidase activity (responsible for the conversion of rutin to the flavonoid quercetin) and there was an associated increase in the capacity of hepatic fractions (S-9) to activate the food pyrolysis products IQ, MeIQ and MeIQx to bacterial mutagens in vitro. Hepatic conversion of aflatoxin B1 to a mutagen was unaltered while in vitro activation of quercetin was significantly lower in tissue fractions from the rutin-fed rats compared with those from controls.

The influence of incubation pH on the activity of rat and human gut flora enzymes.

The activities of three bacterial biotransformation enzymes (beta-glucuronidase, beta-glucosidase, nitrate reductase) were determined in suspensions of rat caecal contents or human faeces over the pH range 6-8. All three enzymes were influenced by pH, as exemplified by beta-glucosidase activity which diminished as pH increased. In other instances the rat and human flora showed distinct profiles, with nitrate reductase activity undetectable in human faeces below pH 6.

Influence of starches of low digestibility on the rat caecal microflora.

1. Male Sprague-Dawley rats were fed on either a purified, fibre-free diet or a diet in which half the maize starch was replaced with uncooked amylomaize or potato starch (equivalent to 100 or 200 g amylase-resistant starch (ARS)/kg diet respectively). Changes in short-chain fatty acids (SCFA), pH, ammonia and a number of bacterial variables in caecal contents were then assessed.