The Non-Sporing Anaerobic Bacteria in Human Faeces

Abstract

DIET has long been assumed to be one of the major determinants of the faecal flora (Dudgeon, 1926). Studies with experimental animals provide support for this hypothesis (Smith, 1965); however, studies with human faeces have provided less satisfactory evidence (Moore, Cat0 and Holdeman 1969).In a study of faecal specimens from different dietary groups in various parts of the world, we demonstrated differences in the numbers of bacteroides organisms present in faeces (Hill et al., 1971). In the present paper we report on the more detailed classification of the non-sporing anaerobes isolated in that study and during subsequent extensions of the study. MATERIALS AND METHODSSource of faeces. Stool samples were obtained from groups of people consuming a mixed western diet, in England, Scotland and the USA, and from people living on diets with a high carbohydrate content in India, Uganda and Japan. The characteristics of these groups are shown in table I. The groups contained both men and women. All were healthy individuals, mostly aged between 20 and 50. Samples from the USA came from both black and white persons.Transport and storage of specimens. Fresh samples of faeces were diluted 1 in 10 in 10% glycerol broth and immediately frozen in solid carbon dioxide or in liquid nitrogen for transport to London (Crowther, 1971). The samples were stored at -50°C.Isolation of non-sporing anaerobic bacteria. Isolation plates were seeded in an anaerobic cabinet. During the initial stages of this investigation a rigid Perspex cabinet filled with oxygen-free nitrogen (N2) containing 5% carbon dioxide (C02) was employed (Drasar, 1967). Later studies were carried out in a flexible polyvinyl cabinet filled with 5% C02 in a mixture of 90% N2 and 10% hydrogen (H2) (Aranki et al., 1969). Ten-fold dilutions of the specimens were prepared in Brain-Heart-Infusion (BHI) broth (Oxoid) containing 0.05% (w/v) cysteine hydrochloride and 0.03% sodium formaldehyde sulphoxylate as reducing agents. The diluent was heated to 100°C before being introduced into the cabinet, where it was dispensed and allowed to cool in the anaerobic environment. 0.1-ml samples of appropriate dilutions were spread on the surface of plates of Reinforced Clostridial Medium (Oxoid) with 1 % glucose (w/v), 1 % liver digest (Panmede, Paines and Byme, Greenford, England) and 10% defibrinated horse blood. In order to maintain the media in a reduced state, the plates were poured and dried in the Perspex cabinet, or stored for 3 days in the flexible cabinet. Seeded plates were packed into anaerobic jars and on removal from the cabinet the jars were re-evacuated and filled with a gas mixture containing 30% C02 and 70% H2 and incubated at 37°C for 3 days. Cold " D " catalyst was used in the anaerobic jars (Englhard Industries, Cindeford, Gloucestershire).

The influence of a diet rich in wheat fibre on the human faecal flora

“…The incidence is high in Western Europe and North America but low in Africa, Asia and most of South America and this is thought to be related to the bacterial production or activation of carcinogens in the intestine. In a previous study, in which the flora of faeces from populations in areas with low and high incidences of colon cancer, bacteroides organisms were shown to be more common in faeces from areas in which the incidence of cancer of the large bowel is high whereas eubacteria were more common in faeces from lowincidence regions (Peach et al, 1974). Bile salts are thought to provide the substrate for the production of carcinogens or co-carcinogens by bacteria.…”

“…As mentioned previously, when the flora of faeces from populations in low-and high-incidence areas was examined, differences were found in the proportion of the various groups of non-sporing anaerobic bacteria isolated (Peach et al, 1974). If these results are to be explained in terms of the intake of fibre it would be expected that a decrease in the numbers of bacteroides .organisms and an increase in the numbers of eubacteria would be seen.…”

“…Ten strains of non-sporing anaerobic bacteria and 10 strains of clostridia were sampled from each specimen. The non-sporing anaerobes were further identified as described previously (Peach et al, 1974). The volatile fatty acid end-products of glucose metabolism were detected with a Perkin-Elmer F.40 Automatic bead-space analyser (Drasar et al, 1976).…”

Faecal steroids and bacteria and large bowel cancer in Hong Kong by socio-economic groups

“…Non-sporing anaerobic bacteria were further identified on the basis of analysis of the acid end-products from glucose (Peach et al, 1974). The sporing anaerobic bacteria (the clostridia) were further identified using the range of tests described by Drasar et al (1976).…”

“…It was postulated that diet would influence both the concentration of bile acid substrate in the large bowel and the nature of the bacterial flora acting on the bile acids, and thus be related to the incidence of large bowel cancer. Support for this view has been obtained in international comparative studies of faecal bacteria and steroids (Hill et al, 1971a;Peach et al, 1974). The faecal steroid analyses have been extended to include 9 countries (Hill and Drasar, 1974).…”