Re: What type of bacteria grow in shoes?

Hi Beth!

You ask a good question.First I will discuss how location affects bacterial growth and form. As with any living organism bacteria need water to grow. Therefore bacterial growth will vary depending on water availability within their immediate location. The skin is a good example of how bacterial growth is related to their location on the skin. Higher bacterial growth is found in places on the skin where moisture can accumulate, for example the armpit or between the toes. On the bare open skin such as the arm the skin is quite dry, bacterial growth is present but low. The bacteria found on such dry surfaces must take a different form to survive. These bacteria are better suited to handle the dry surface and they will not easily dry out. Another important factor relating location to bacterial growth is the amount of food available to the bacteria. On our skin there is little food available however bacteria growing in our mouths have much more food available to them. As a result bacteria grow better in our mouths than on our skin. Tiny bits of food (that bacteria also use as food) remain in our mouth after we have eaten therefore bacteria in our mouths have access to a continual supply of nutrients. The main point to remember is that the amount of bacterial growth will vary depending on the availability of water and food in their immediate location. A good URL that elaborates on the growth and types of bacteria found on different locations on the body can be found here.

An interesting experiment to try is to compare the numbers of bacteria growing on different locations on your skin. Using a sterile wetted Q-tip rub a small surface of your forearm and then streak the Q-tip on a nutrient agar plate (ask a teacher if you can get some nutrient agar plates from a university or hospital near your school). Using another Q-tip perform the same procedure but this time rub the Q-tip in your mouth. Compare the numbers of bacteria growing from the two different locations. Which location do you think would contain more bacteria?

Bacteria found in shoes are not likely to be dangerous. The bacteria found in your shoe would probably be the same type found growing on your feet. Examples of the major bacteria growing on our feet are Staphylococcus, Micrococcus and Corynebacteria. Since these bacteria normally live on our skin they should not be dangerous. The bacteria may cause rare infections in people with damaged immune systems. A link to another Mad Scientist question/answer that elaborates on foot bacteria can be found here.

I hope this information helps you, Beth and I hope you continue to explore the interesting world of microbiology!

Chris