Catherine E. Bayliss

Intestinal microflora, morphology and enzyme activity in zinc-deficient and Zn-supplemented rats

1. Immature, male Wistar rats were given a low-zinc diet (2 mg/kg) for 22-24 d. Control groups received a similar diet supplemented with 58 mg Zn/kg either ad lib., or in amounts matched to the consumption of the Zn-deficient group. Food consumption, rate of growth and food conversion efficiency were markedly lower in the Zn-deficient group of rats compared with controls. Appetite, growth rate and food utilization improved dramatically over a subsequent 4 d period of Zn supplementation. 2. Morphological examination of samples of jejunum and ileum confirmed that Zn deficiency in the rat is accompanied by a reduction in villous dimensions and increase in villous density. After a short period of Zn supplementation, villous density and the basal width and maximum height of individual villi in the jejunum returned to normal. Similar changes occurred in the ileum but to a lesser extent. 3. Mucosal alkaline phosphatase (EC 3.1.3.1) activity was significantly lower in the small intestine of Zn-deficient rats compared with Zn-supplemented rats. Disaccharidase activities were lower in the Zn-deficient group, compared with their feed-restricted counterparts, but were similar to values for ad lib.-fed controls. Tissue alkaline phosphatase and disaccharidase activities were consistently higher after a 4 d period of Zn supplementation, compared with non-supplemented animals, but this increase was only significant for alkaline phosphatase. 4. Although there were striking similarities in the mucosal characteristics of gnotobiotic and Zn-deficient rats, there was no indication that even severe dietary Zn depletion reduced the numbers of viable bacteria present in either the small or large intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Examination of organisms associated with mucin in the colon by scanning electron microscopy

Abstract Different preservation techniques were compared to investigate changes introduced into rat colonic mucosa as a result of chemical treatment and dehydration prior to examination using the scanning electron microscope (SEM). Rapid fixation with osmium vapour followed by freeze-drying produced samples closest to the in vivo appearance, but the use of liquid fixatives, particularly when combined with solvents currently in use prior to critical-point drying, enabled successive layers of oraganisms to be seen beneath the top surface of the mucin. Use of the sputter cryo attachment to the SEM to provide further detail from freeze-fractured material is discussed.

The effect of dietary fibre on bacterial densities in the rat intestine

Abstract When non-absorbable food polysaccharides were included in the diet of rats, changes in the distribution of bacteria in intestinal contents were seen. Male Wistar rats were fed a starch-containing fibre-free diet, or a similar diet in which guar gum (40 g kg −1 ) or cellulose (100 g kg −1 ) were substituted for an equivalent portion of starch. A fourth group received a commercial pelleted feed. After a 4-week feeding period, the densities (viable count per g contents) of aerobic and anaerobic bacteria in the lumen of the small intestine and caecum were estimated and the concentration of short chain fatty acids (SCFA) in the caecal contents measured. The proximal small intestine from the pellet-fed and the guar-fed rats contained a significantly higher density of anaerobic bacteria than the fibre-free group or the rats fed cellulose. In the caecum, the guar-fed rats had a higher density of anaerobic bacteria than the fibre-free controls, whilst the cellulose-fed group had a lower density. SCFA concentrations in the caecal contents of these three groups were similar. However, although the concentration of SCFA in the caecal contents of the pellet-fed animals was higher than any other group, the density of bacteria was significantly lower than in either the guar-fed or fibre-free animals. It was concluded that dietary fibre influences the distribution of anaerobic bacteria in the small intestine of the rat and alters both the numbers of bacteria and the level of SCFA in the caecum.