A research team led by Jiyoung Ahn from the New York University School of Medicine analyzed the complete bacterial DNA from stool samples of 47 CRC patients and 94 healthy volunteers and were able to identify the complete spectrum of intestinal bacterial species.

They found that the healthy volunteers had a higher diversity of bacterial types than the sick patients. In healthy subjects, the proportion of clostridia was ten percent higher. Some members of this bacteria group break down fibre (cellulose), releasing butyric acid, which has an anti-inflammatory effect. On the other hand, the assumption is that a large number of other bacteria could be able to trigger inflammation and increase the likelihood of disease.

Thus the levels of Fusobacteria and Porphyromonas bacteria were higher in the samples from the cancer patients. Members of both microbial groups are pathogens for dental infections and could contribute to inflammatory bowel diseases, according to the scientists.

Source:
http://www.wissenschaft-aktuell.de/artikel/Koennen_Bakterien_Darmkrebs_beguenstigen_1771015589425.html

The researchers have published their findings in the Journal of the National Cancer Institute:
Jiyoung Ahn et al (2013): Human Microbiome and Risk of Colorectal Good Cancer. Journal of the National Cancer Institute, DOI: 10.1093/jnci/djt300.