We Have the Control

Microbiologists study a number of very interesting places in our world. One such very interesting yet somewhat disgusting place is the microbial world inside our intestines.

Many people don't want to even think about this aspect of our lives. However, a healthy bowel is very important. When the bowels (intestines) do not function properly people suffer tremendously.

The bacteria residing in our intestines play an important role in health and disease. The intestines contain a very complex ecosystem. There are from 2-4 pounds (1-1.5 kg) of bacteria in our intestines. From 100 billion to 1 trillion bacteria are in each gram (0.03 ounces) of feces (poop). There are from 400 to 500 different kinds (species) of bacteria in the intestines.

Previous studies have demonstrated that the composition of the bacteria in the intestine remains quite stable over long periods of time. It appears that diet, medical treatments and stress can affect the bacterial composition in the intestines (intestinal flora). People with Crohn's disease (an inflammatory disease of the intestines) and rheumatoid arthritis (an inflammatory disease of the joints) have an altered intestinal flora.

However, a recent study in Infection and Immunity has demonstrated that our bodies also control what bacteria dwell in our intestines. Studies that characterize the intestinal flora can be very difficult. Imagine trying to identify 400-500 different bacteria. This is nearly impossible. To do this particular study these researchers from the Department of Medical Microbiology, Turke Immunology Centre, Turku University, Turku, Finland, decided to look at the fatty acids in the membranes of bacteria that dwell in mouse intestines.

It has been shown that each type of bacterium makes unique membrane fatty acids. Using gas-liquid chromatography P. Toivanen and associates were able to determine the total bacterial fatty acid composition in the feces of mice. This approach provides a much quicker way to determine changes in the bacterial flora of the intestine.

The researchers then took mice that were genetically identical (much like identical (monozygotic) twins, they have all the same genes) and determined what bacterial fatty acids were in the feces. These genetically identical mice all had pretty much the same bacterial flora in their intestine. They then took mice that were different only in one set of genes called the major histocompatibility complex genes (MHC). These MHC genes code for proteins that are on the surface of nearly all the cells of the mouse.

The MHC proteins help them to differentiate between their own cells and foreign cells. When they looked at the bacterial flora in mice that had different MHC proteins they found major differences in the bacteria dwelling in these two slightly different mice.

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