A human microbiome is the composition of microorganisms on and in a human. This microbiome can be assessed based on the genes of all of the microorganisms on and in the human, or based on the microorganisms themselves. In both cases, the human microbiomes vary person to person and even within the same person over their lifetimes. In a recent study, specific-pathogen-free mice were injected with Azoxymethane (AOM), a chemical carcinogen, to induce colon tumors.
One group of mice were given a cocktail of antibiotics, while another cohort were not. The ones treated with the antibiotics tended to not develop tumors, while the ones without the antibiotics developed a number of tumors. The colon microbiome, or composition of the microorganisms in the mice colons, varied throughout the study based on the treatment the mice were given. Not all mice who developed tumors had the same bacteria noticeable in their colons, but they all exhiubited a shift in the types and diversity of the bacteria in their colons.
Although more research is still needed to fully understand how the microorganisms interact with each other and the host, the concept of a shift in the microbiome based on the health of the individual is clear. The shift might help cause the health change, or it might be an effect of the change. Either way, knowing more about the microorganisms which we live with and need to survive will help us understand trends involving disease progression.
The Human Genome Project and Cancer 