Identification of Organisms That Make Up the Microbiota

A very large percentage of the microorganisms populating the intestine cannot be cultured. Thus the study of the microbiota now generally involves extracting DNA from a stool sample and identifying both anaerobes and aerobes using genetic techniques. The genetic studies have raised questions about the concept of bacterial species. There is much genetic exchange, and the relationship of different molecular signatures to different bacteria is not completely clear. Morris indicated that a tremendous revolution is just beginning to occur in our understanding of the composition of microflora of the human gastrointestinal tract.

Although Mai focused his discussion on the potential role of bacteria in the development of colorectal cancer, his group has not ruled out a potential role for yeasts. However, because the number of yeasts per person is much smaller than the number of bacteria (on the order of 105 or 106 for yeast, compared with 1011 or 1012 for bacteria), few yeasts are found in microscopic studies of the gut microflora. Special methods will be needed to study the involvement of yeasts.

Future Directions

The evidence suggests that very complex metabolic and biochemical reactions are occurring continually within our intestines and that disturbances of the microbiota might substantially change a person’s ability to handle specific toxins, metabolic by-products, or other substances in the intestine. This subject lies within the intersection of foodborne disease, the bacteria in the intestines, and the occurrence of chronic disease. Morris said that there is a need to conduct studies in locations outside the United States in order to understand the differences that may arise in different geographic areas. Considering the development that Iran is undergoing, Mai suggested that it could be a promising region for the study of a variety of factors that affect the risk of developing colorectal cancer. Such study also would have the benefit of helping identify the environmental causes of cancer that could be controlled.

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