First, touch a commonly used surface like a doorknob or phone. Then, use a sterile cotton swab to collect bacteria from their unwashed hands. Next, rub the swab onto three separate petri dishes. Label each dish accordingly. Now, have the person wash their hands with three different soaps, After washing, use a new sterile swab to collect bacteria from their hands again. Rub each swab onto a new set of petri dishes. Leave all petri dishes in a warm place for 24 hours. to see the bacterial growth to see which soap was most effective.