Composition Of The Adult Fecal Microbiota Assessed By Culturing

Much of the early information on the composition of the human colonic microbiota was elucidated using traditional cultivation techniques. The majority of such work was driven by the quest to determine the relationship between diet and colonic cancer (16,36-38). Epidemiological studies had identified that risk of colon cancer correlated with dietary habit, with higher colorectal cancer incidence in populations consuming a high-fat, low-fiber diet. In 1969, Aries and coworkers (39) postulated that this correlation between diet and cancer should be reflected in the composition of the colonic microbiota. Thus, interest in the effect of diet on the GI microbiota began in earnest. The majority of these early studies compared the fecal microbiota of individuals from different populations which had significantly different incidences of colon cancer. For example, Aries and coworkers (39) compared the fecal microbiota of English subjects (relatively high incidence) to that of Ugandans (low incidence). Significantly higher numbers of Bacteroides and bifidobacteria were enumerated from English individuals (Table 1), whilst enterococci, lactobacilli, streptococci, and yeasts were present at higher numbers in the fecal microbiota of Ugandan subjects. Subsequent studies compared the microbial compositions of multiple populations with either a high or a low incidence of colon cancer (38). Again, higher yields of bacteroides were seen for the high-risk populations (Table 1). However, an even more striking observation was the higher anaerobe-to-aerobe ratio in fecal samples from the high-incidence populations. Moore and colleagues (40) similarly showed higher levels of Bacteroides and bifidobacteria in subjects from high-risk populations (North Americans), when compared to low-risk populations (Africans). However, these observations were not consistent for a second low-risk population (Japanese) for whom the greatest percentage of isolates was Bacteroides (Table 2). More detailed characterization of these isolates identified that Bacteroides vulgatus, Bacteroides distasonis and Peptostreptococcus productus (reclassified as Ruminococcus productus) were the more predominant members of the fecal microbiota of high-risk populations (40). In addition, a notably higher percentage of isolates in the low-risk populations belonged to the species Bacteroides fragilis, Eubacterium aerofaciens (reclassified as Collinsella aerofaciens) and Escherichia coli (Table 2). Such detailed analyses of the microbial community have highlighted the

Table 1 Investigations of the Bacterial Composition of Fecal Samples Collected from Individuals from Countries with High or Low Incidence of Colon Cancer

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