WITH the development of effective anaerobic techniques, the composition of the human intestinal bacterial flora is now more clearly understood. Although the detailed composition is dependent on the nature of the diet (see, for example, Hill et al., 1971), in all cases studied the predominant faecal bacteria are those of the non-sporing strictly anaerobic groups. The metabolic significance of the gut flora is only slowly emerging, but a number of review articles (e.g., Smith, 1966;Scheline, 1968) attribute to it a wide range of reactions of toxicological interest.The involvement of intestinal bacteria in such reactions is usually inferred from indirect evidence-for example, the effect of antibiotic treatment on the metabolism of the drug, or the comparison of germ-free and conventional animals-and there are few direct studies using pure strains of bacteria. In particular, the metabolic activities of the non-sporing strictly anaerobic bacteria are virtually unknown.Many of the enzymes concerned in the metabolism of food additives and drugs are already well known to bacteriologists. For example, the /%glucosidase responsible for the hydrolysis of aesculin and salicin is also responsible for releasing the active agents from some cardiac glycosides (Lauterbach and Repke, 1960), from cascara sagrada (Fingl, 1965) and from cycasin (Spatz, McDaniel and Laqueur, 1966).In the process of detoxification, many compounds are conjugated by the liver to form, for example, glucuronides, and then excreted in the bile into the intestine (Smith, 1966). The glucuronides may then be hydrolysed either by enzymes of the gut mucosa or by enzymes of any bacteria present in the gut, releasing the aglycone, which may be reabsorbed and may be subsequently re-excreted by the liver into the gut.Escherichia coli is well known to produce a /3-glucuronidase (Buehler, Katzman and Doisy, 1951), but E. coli normally constitutes only a small proportion of the gut flora and there are no quantitative studies on the relative contributions to the glucuronidase activity of the gut contents by various bacteria. Similarly the contributions of the different bacterial species to the total activity of other glycosidases in the gut have not been assessed.We have therefore examined the gut flora of four laboratory animals commonly used in toxicological studies and estimated the activity of the glycosidases produced by the principal groups of intestinal bacteria.
MATERIALS AND METHODSCharacterisation of the gut flora. All the animals examined were fed ad libitum-rats and mice on diet 41B (Oxoid), rabbits and guinea-pigs on diet SG1. The rats, mice and guineapigs were killed with chloroform and the rabbits by intravenous injection of air. Immediately
(1971) 451Downloaded from www.microbiologyresearch.org by after death the abdomen was opened and the gastro-intestinal tract was ligatured at the oesophagus, at the duodenum at a point close to the stomach, at various points along the small intestine, at the ileo-caecal junction and at the rectum. After removal of t...
