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...

The correlation between cancer of the breast, colon and stomach dietary factors, and various indicators of standard of living was examined. Cancer of the breast and colon was highly correlated with fat and animal protein.

An investigation was undertaken to determine whether Acanthamoeba polyphaga SHI and Naegleria gruberi 1518/1e could affect the survival of various strains of Vibrio cholerae in laboratory microcosms. In microcosms pre-inoculated with trophozoites of amoebae, all six strains of V. cholerae tested survived and multiplied during 24 h. In control microcosms without trophozoites of amoebae, survival of the V. cholerae strains was much decreased. Two strains of V. cholerae were used to determine whether V. cholerae might survive ingestion within amoebae and subsequent encystment. Strain 152 was re-isolated from encysting N. gruberi 1518/1e but not from A. polyphaga SHI. Strain 9112 could not be isolated from cysts of either species of amoebae.

SUMMARYThe survival and growth of toxigenic Vibrio cholerae 01 in water under various conditions of salinity, pH, temperature and cation composition and concentration were studied in an extensive series oflaboratory experiments. Inter-and intra-strain variation in stress response (of 01 and non-01 strains) and the ability of V. cholerae to adapt to stressful environments were also studied. Toxigenic V. cholerae 01 were able to survive for at least 70 days at 25°C in solutions of sea salt. The optimal salt concentration was 2-0 % though all solutions in the range 0-25-3-0 % gave good support. Substrains with enhanced capacity to persist at sub-optimal salinity (0 1%) were demonstrated. A great degree of inter-strain variation in stress response at low salinity (0 05 %) was found among 59 strains, and this variation was unrelated to serogroup (01 or non-01), source (clinical or environmental) or country of origin (Tanzania or Bangladesh). At optimal salinity, inter-strain variation was less and 18 out of 20 strains remained viable at high concentrations for at least 40 months at 25 'C. V. cholerae 01 could not survive beyond 45 days at 4 'C and optimal salinity, either with or without nutrients. The optimal pH range for survival at 25 'C was 7-0-8-5 at optimal salinity, and 7 5--90 at low salinity. V. cholerae 01 require Na+ for survival in the absence of nutrients, and for enhanced growth in their presence. The presence of Ca2+ or Mg2+, in addition to Na+, further enhanced survival. These, and other results reported in this paper, suggest that toxigenic V. cholerae 01 are able to survive for extended periods in warm water containing no nutrients but having a salinity of 0-25-3-0 0% and a pH of around 8-0. With added nutrients and under the same conditions, rapid growth is possible. The implications of these findings for the identification of putative aquatic reservoirs of V. cholerae 01, and for the epidemiology of cholera, are considerable.