Bacteria in poultry meat
The hypothesis that irradiated chicken has the least amount of bacteria growing on it is proven to be true.
The science fair project can be repeated by varying the types of food/ parts of the meat that are tested for bacteria. Perhaps you could experiment with different methods of thawing meat, or evaluate whether the type of packaging used for the meat affects the bacteria count.
The truth about irradiated meat - http://www.mindfully.org/Food/2003/Irradiated-Meat-TruthAug03.htm
Bacteria that cause food borne illness - http://www.infoplease.com/ipa/A0762206.html
Always follow laboratory safety guidelines and always practice sterile technique when handling microbes. Never have any food or drink at your workstation and always thoroughly wash your hands with disinfectant soap or alcohol before leaving your workstation. Always dispose of used material in a biohazard bag. If none are available, the bacteria should be destroyed with bleach before being disposed of. Knives should be handled under adult supervision.