Discussion of Current Bacteriological Investigations of the Relationships between Intestinal Flora, Diet, and Colon Cancer'

Epidemiological data have indicated a correlation be tween dietary components, especially beef or beef fat, and the incidence of colon cancer. Epidemiological data also indicate that individuals from low-risk populations who adopt the food habits of high-risk populations do develop the higher risk, and it is reasonable to postulate that the intestinal flora may produce or potentiate carcinogens or cocarcinogens, although the specific substrates or products are unknown. It has been assumed that the kinds of bacteria present in the intestinal tract are primarily controlled by dietary intake. Several years ago, Hill et a! (I, 7) surveyed the fecal bacteria of populations with different meat con sumption and reported that they found a correlation between the general kinds of bacteria in the feces and risk to colon cancer. To evaluate the relationship between colon bacteria and colon cancer, in 1971the National Cancer Institute initiated 2 of the most extensive studies of the fecal flora ever undertaken, I in Dr. Finegold's laboratories in California and 1 in our laboratories at Virginia Polytechnic Institute. In 1971 there were no good base-line data available concerning the kinds of bacteria in human feces.This is not surprising, because only I to 2% of the fecal bacteria had been cultured (or were known to be viable) before 1960. Between 1960 and 1970, after methods adequate for culture of fecal bacteria were developed, no comprehensive study of the bacteria in feces of normal individuals was done, largely because of the expense involved. Enough work was done during this decade, however, for us to realize that the fecal flora was much more complex than we had initially thought. In his studies, Dr. Finegold (5) has used a battery of selective and nonselective media to look for groups of species whose incidence may differ significantly between highand low-risk populations. We have used nonselective media and statistically randomized sampling to determine the composition of the fecal flora of populations at different risks. With the sample size studied, we detected the relative proportions of the kinds of bacteria that statistically account for 60 to 80 % of the total cultivable bacterial population in an individual fecal specimen. On the basis of comparisons of microscopic and cultural counts, we cul tured 70 to 95% of the bacteria present (8, 10). We have studied fecal samples from 20 individuals in each of 5 populations representing 3 â€œriskgroups. â€• Japanese Hawaii ans from whom adenomatous polyps had been removed represented the high-risk population; a cohort Japanese Hawaiian group and normal North Americans represented the moderately high-risk group; and rural Japanese, and Africans of the Tswana tribe, each on their native diets, represented the lOw-risk populations (3). We have also examined the effects of 3 extreme diets on the fecal flora of 5 North Americans, and we are presentlystudying the flora of 8 anatomical areas of the gastrointestinal tracts of 6 North Americans. Although the experimental designs of Dr. Finegold's project and our project differ, the results from each study may be used to confirm observations of the other study. Thus far, like Dr. Finegold, we have not been able to confirm reports that individual species or genera correlate with risk of colon cancer. Both bacteroides species and clostridial species have been implicated by other workers3 (1, 6, 7), but the concentrations of these bac teria in our high-risk groups are intermediate between the concentrations we find in the African or Japaneselow-risk groups. Bacteroides species are more numerous in the feces of the native Japanesethan in the polyp patients, while clostridial species are more numerous in the floras of Africans than in the polyp patients. From our experiments, it appears that some of the differences in fecal floras that were reported from the early survey work may have occurred as a result of the procedures used to transport specimens from different geographic areas to the laboratory for analysis. Therefore, all of our culture work wasinitiated within a few minutesof samplecollection in each geographic location. Most of the work in intestinal bacteriology has been done with the fecal flora. Fortunately, our studies ofthe flora of 8 anatomical areas of the gastrointestinal tract indicate that the fecal flora is, indeed, representative of the flora of the ascending, transverse, and descending colon and rectum, where the carcinogenic activity presumably takes place. In these same studies of autopsy material taken within 4 hr of