The projects you are talking about are just ideas to get you to begin to think. It is important to do a science fair project that is about something you are really interested in. If you are really interested in bacteria, there are numerous investigations that you can perform. First, answer the question "What is it about bacteria that really interests me?" (Are you interested in bacteria that eat oil, how bacteria reproduce, the effect of antibiotics on bacteria, etc.) Once you answer this question, you can find a really good experiment that you will enjoy doing.
Good Luck. Feel free to ask any furthur questions that you might have!