Bacteria and sweat
The hypothesis that the amount of bacteria in shoes will be higher if they are worn without socks, is proven to be true.
The smell from our feet can be reduced by wearing cotton socks that are able to absorb sweat more effectively, and also by properly airing our shoes. The bacteria count can be lowered by frequently changing socks and washing our feet with antibacterial soap.
This science project can be repeated by wearing socks made from different materials like cotton or polyester.
Modify the science project by using shoes made from different materials like leather, PVC, etc.
Why do feet stink? - http://health.howstuffworks.com/skin-care/information/anatomy/question5141.htm
What causes smelly feet? - http://www.brighthub.com/science/genetics/articles/48373.aspx
The bacteria should be destroyed before the swabs are discarded. Pour some bleach into the petri dish to kill all the bacteria before disposing in the trash.