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The effect of hydrogen peroxide on the germination, colony formation and structure of spores of Clostridium bifermentans was examined. Treatment with 0.35 M-hydrogen peroxide increased the germination rate at 25 "C but increasing the temperature or concentration of hydrogen peroxide decreased both the germination rate and colony formation. The presence of Cu2+ increased the lethal effect of hydrogen peroxide on colony formation as much as 3000-fold. Preincubation of spores with Cu2+ before treatment with hydrogen peroxide produced a similar increase, but this could be eliminated by washing the spores with dilute acid or ethylenediamine tetraacetate. Hydrogen peroxide removed protein from spores-apparently from the coat-and treatment with dithiothreitol, which also removes spore-coat protein, increased the lethal effect of hydrogen peroxide 500-fold, suggesting that spore-coat protein has a protective effect against hydrogen peroxide. (1940) first showed that the rate of loss of viability of spores in the presence of hydrogen peroxide depends on temperature and pH. Copper and cobalt ions increase the lysis of spores by hydrogen peroxide (Gould & Hitchins, 1963) but their effect on spore viability and structure has not been examined. We have therefore studied the effect of pH, temperature and the concentration of hydrogen peroxide and metal ions on colony formation, germination and the structure of spores of Clostridium bifermentans. METHODSOrganism, spore preparation and maintenance of culture. The strain of Clostridium b fermentans used and the preparation and storage of spores were as described previously (Waites & Wyatt, 1971) except that spores were produced on a trypticase agar containing (g 1-l): Trypticase (BBL), 30 ; yeast extract (Difco), I '0 ; ammonium sulphate, 10 ; agar, I 2 ; adjusted to pH 7-3 with I M-NaOH. The organism was maintained in the reinforced clostridial medium of Hirsch & Grinsted (1954).Treatment of spores with hydrogen peroxide. Hydrogen peroxide (BDH) at the concentrations described was added to spores (about 0.7 mg dry wt ml-l) in sodium phosphate buffer (100 mM in phosphate at the stated pH) which had been pre-incubated at the required

Ultra‐violet (u.v.) light irradiation of spores of Bacillus subtilis in the presence of hydrogen peroxide produced a rapid kill which was up to 2000‐fold greater than that produced by irradiation alone. A kill of 99–99% was produced by 30s u.v. irradiation of spores of 6 strains of Bacillus and Clostridium in the presence of hydrogen peroxide 1.0 g/100 ml but with the more resistant spores of 9 further strains, irradiation in the presence of hydrogen peroxide 2–5 g/100 ml followed by mild heating was required.

1. Gum arabic is a water-soluble polysaccharide resistant to human gut enzymes and thus can be described as dietary fibre.2. Using a most-probable-number technique, estimates were made of total anaerobes and of gum-arabic fermenters in the faeces of a volunteer during a contro1 period and during addition of 10 g gum arabic/d to the diet. Using an enrichment technique, the principal bacteria able to utilize gum arabic as the only carbohydrate source were isolated and characterized. 3. Faecal samples were analysed for undegraded gum arabic and, following acid-hydrolysis, for total sugars. 4. The proportion of the faecal flora able to degrade the gum arabic polymer rose from an initial level of 6.5% to more than 50% during gum-arabic ingestion, and subsequently returned to the control level after ingestion ceased. The principal gum-arabic fermenters were species of Bucteroides and Bifdobucterium.5 . Undegraded gum arabic was not detected in any faecal sample nor were there significant differences in the level of total sugars in acid-hydrolysed faeces between gum arabic and control periods.6. The results presented indicate a direct and rapid change in faecal flora in response to a specific change in the diet of a human volunteer.Little change in human faecal flora has been detected following changes in diet (Moore et al. 198 1 ; Savage, 1982) and studies have been complicated by the differences in flora seen between individuals. It is possible, however, that although no gross changes in the species occur, the population may adapt to the presence of new substrates by a change in the biotypes present or in other ways.Dietary fibre, which has a marked effect on the function of the large intestine, increasing faecal weight and reducing transit time (Eastwood & Passmore, 1983), includes the plant gums widely used as thickening, gelling and emulsifying agents in the food industry. Previous work has shown that inclusion of guar gum in the diet of a human subject increased the total count of anaerobic bacteria in faeces (Bayliss & Houston, 1985).Gum arabic is the second most widely used gum in the food industry (Blenford, 1984) and as such forms part of the average Western diet, although at a low level. It is a highly water-soluble extract from Acacia senegal, and is a high-molecular-weight globular molecule with a backbone of D-galactopyranose units and complex side chains of D-galactose, L-arabinose, L-rhamnose and D-glucuronic acid. The in vivo effects of gum arabic in the diet have been demonstrated by McLean Ross et al. (1983), who showed that breath hydrogen increased in subjects who had eaten a diet containing gum arabic for 3 weeks but not in control subjects whose diet had not contained gum arabic. It seems likely that this increase reflected an adaptation of the microbial population of the human colon to the presence of the substrate. Therefore, the present study was carried out to determine whether a specific change in the diet of a human volunteer could lead to a change in faecal flora or in that part of the flo...