Science Buddies: "Ask an Expert"

My experiement is to test surfaces in the house for bacteria. The teacher says to do more than on Petri dish for each surface. How many do I need to do for each surface and how do I collect the sample - do I use one q-tip and rub it on two or more Petri dishes or do I use more than one q-tip and test different areas of the same surface?

My recommendation would be to use 2-3 petri dishes for each location. That way you have more data to observe. Identify a number of areas you would like to swab such as kitchen sink, bathtub etc...the more variety the better. For each location take a Q-tip and rub it around the area and then onto the agar on your petri dish. Each Q-tip sample should go onto a separate dish. Don't forget to label the dishes with the locations so you know what growth came from where. Hope this helps. Have fun watching what grows. You will be surprised!