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Good Bacteria

Around 1000 species of good bacteria live on our skin according to a study in the May 23, 2009 issue of Science.

The scientists expected to find the most bacteria in moist dark environments such as our underarms, between our toes, or what they delicately called our "gluteal crease."

Surprisingly, the greatest diversity of bacteria was found on our forearms.

Bacterial cells are much smaller than typical human cells, so even though most of our body by weight is made up of human cells, we have about ten times more bacteria living on or in our body than there are human cells.

Although some of these bacteria can make us sick, most are harmless, and many are beneficial.

Traditionally, scientists have counted the number of bacteria living in and on the human body by swabbing parts of the body with a sterile Q-tip, and then using petri dishes to grow the bacteria in an incubator.

In this study, instead of trying to grow the bacteria, they used modern DNA technology to identify the species. Most of the bacteria that live on our skin don't grow well in an incubator, so scientists were surprised to find that around 1000 different species of bacteria live on the human skin.

With an incubator, some Q-tips and petri dishes, you can repeat the study, and see how many bacteria you are able to grow from the human skin. My hypothesis would be that without DNA technology, you will find the most bacteria growing on moist parts of the body, such as between the toes.

Here are some important safety considerations:

  1. Set the incubator a few degrees below 98.6 F (37 C). Although this will lead to fewer bacterial colonies, disease causing bacteria often grow better at body temperature.
  2. Do not open the petri dishes to count the colonies. Instead try to count the colonies from underneath.
  3. Dispose of the petri dishes in a plastic bag filled with lysol.
  4. Do not collect samples from the mouth, nose, or gluteal crease.
  5. Do not collect samples from any section of the skin which seems infected.

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