Organisms able to grow on arabinogalactan, pectin, xylan, wheat bran, guar, apple cell walls, and mucin were isolated by enrichment from human feces. The number of polysaccharide fermenters and the properties of the predominant bacteria varied between subjects. The ability to use one polysaccharide was not related to the ability to use others. Some organisms (e.g., Bacteroides spp.) isolated on other substrates also utilized mucin, but were not isolated in the mucin enrichment. The mucin fermenters isolated by enrichment had a very restricted ability to utilize complex polysaccharides and their constituent monosaccharides, suggesting that the presence of plant polysaccharides in the human colon is unlikely to prevent the use of colonic mucin as an energy source by bacteria. Characterization with a range of biochemical tests showed that many of the isolates, but especially the mucin fermenters, did not resemble organisms described previously.
The microorganisms associated with the undiseased human colon wall were examined in material obtained from four sudden-death victims. In traffic accident subjects (aged 45 and 16 years) the anaerobe-aerobe ratio was about 10 4 :1 in all areas of the colon examined, whereas in acute heart failure subjects (aged 74 and 46 years) the ratio was as low as 1.2:1. The flora of each individual was distinct and complex. Although the predominant anaerobes isolated were Bacteroides and Fusobacterium spp., which composed over 50% of the flora in some samples, the species isolated (indicated by morphology and glucose fermentation products) varied between individuals. Other major types observed were gram-positive nonsporing rods, including Bifidobacterium spp., and anaerobic cocci (between 8 and 20% of isolates). Clostridia were only isolated in significant numbers from one individual. Scanning electron microscopy showed that most of the organisms were present below the top surface of the mucin layer overlying the mucosa. The use of several different preparative procedures for microscopy showed a complex microbial structure within the mucus, but major variations in the bacterial populations in different areas of the colon were not found. Spiral-shaped organisms up to 60 μm long in the form of double helices were found in two subjects by scanning electron microscopy but were not isolated during the parallel bacteriological investigation. The differences between this and previous studies are discussed in relation to experimental procedures and also in contrast to results with animals that showed a particularly specialized flora associated with the colon wall.
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