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Effects of Dietary Cellulose and Psyllium Husk on Monkey Colonic Microbial Metabolism in Continuous Culture¹

Department of Food Science and Human Nutrition ^* Department of Animal Sciences, Washington State University, Pullman, WA 99164-6320

The effects of inoculating an in vitro continuous culture system with primate colon contents compared to fecal material, and the effect of feeding these cultures psyllium husk, a fermentable, or cellulose, a less fermentable, dietary fiber were tested. Modified 500-ml Bellco culture chambers were continuously infused with buffered medium containing vitamin mix, deoxycholate, urea, hemin, casein and mucin. Cultures were fed a mixture of minerals, sucrose, starch and either psyllium husk or cellulose twice daily. Chambers were inoculated with fecal or colonic samples obtained from adult male African green monkeys fed the respective fiber source in a purified diet for more than 3 yr. After a 5-d stabilization period, samples were collected for total viable anaerobe and aerobe counts, microbial ß-glucuronidase (EC 3.2.1.31) activity, volatile fatty acid (VFA) and ammonia nitrogen concentrations, dry matter, pH and oxidation-reduction potential. Inoculation with fecal material or colon contents produced similar results for the above mentioned characteristics; major differences were found due to the fiber treatments. Psyllium-fed cultures had lower pH (P < 0.01) and higher VFA concentration (P < 0.01) and ß-glucuronidase activity (P < 0.10) than cellulose-fed cultures. The ratio of anaerobes to aerobes was lower (P < 0.01) in psyllium-fed than in cellulose-fed cultures. These results indicate that feces can be used as an inoculum source for in vitro studies of changes in colonic microbial metabolism due to diet, and that dietary fiber source affects the colonic microbial population and metabolism.

KEY WORDS: • continuous culture system • dietary fiber • primate colon microflora • African green monkeys • cellulose • psyllium husk

¹ Presented in part at the 1985 Annual Meeting of the Northwest Branch of the American Society for Microbiology.

² To whom correspondence and reprint requests should be addressed.

Manuscript received 22 March 1988. Revision accepted 17 February 1989.