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Purpose: Does bacteria become more resistant to an antibiotic when exposed repeatedly to it? BACKGROUND: Antibiotics are substances that are produced by molds or bacteria and that kill or inhibit the growth of other microorganisms. Antibiotics specifically attack bacteria without harming cells belonging to the organism that produced them. Antibiotics such as penicillin kill bacteria by inhibiting them from making cell walls that are needed for their survival. Without their cell wall the contents of the cells leak out and the cell is destroyed. Human and animal cells don’t require a cell wall in order to survive, thus these antibiotics do not damage them. While antibiotics are very powerful in the cure of many bacterial diseases, some bacteria have developed ways to resist antibiotics. The extensive use of antibiotics (unfortunately including the over-prescription and misuse of these medications) has resulted in the evolution of bacteria that are not be killed by antibiotics and these bacteria once again threaten health and life. Diseases that were virtually eliminated with the introduction of antibiotics are becoming more and more difficult to cure. Each and every one of us has the ability to help with this ever increasing problem. EXPERIMENT# 1 MATERIALS: • One sterile agar plate labeled with letter A (for antibiotic added) • One sterile agar plate without writing on it (antibiotic free plate) • Objects of your choice to test for the presence of microorganisms: a penny, keys, pens, etc. • Q-tips (to get bacteria from teeth, sandwiches, fruit juice, etc.) • toothpicks • markers for labeling EXPERIMENT# 1 PROCEDURE (FIRST WEEK) 1: Get one of each type of agar plate and label it on the bottom with your name, date, and the origin of your bacteria. You may want to divide the plate into sections by drawing lines on the bottom of the plate (on the outside) and trying different objects in each section. 2: Open the cover of the plate and gently press your object on the surface of the agar. Be careful not to press too hard – you don’t want to press through the agar. Make sure to label what object you used in each section. If you want to try testing food, drinks, your teeth, etc., then wet the Q-tip with the object, and rub the Q-tip on the surface of the agar. You can also use a toothpick. 3. Cover the plate as soon as you remove your object, the Q-top, or the toothpick. You want to have the lid open for as little time as possible so microorganisms from the air do not fall on the plate. 4: Write a hypothesis about what you think will happen on each of your plates. Your plate will be left at room temperature until next week so that any bacteria that are present can grow into colonies. EXPERIMENT# 1 PROCEDURE (SECOND WEEK) 1. Record what you observed on each of your plates. 2. Give an explanation for why you did or did not see growth on the plate that had the antibiotic added to the medium. 3. Discuss how you might be able to help preventing a further increase in antibiotic resistant microorganisms. EXPERIMENT# 2 Because of the increased occurrence of antibiotic resistant bacteria a doctor might test which antibiotics the disease causing bacterium is sensitive to before writing a prescription. Today we will use an assay, similar to the one the doctor would perform, to determine whether the Escherichia colibacterium (a harmless bacterium growing in our gut) is sensitive or resistant to the antibiotics penicillinG and tetracycline. EXPERIMENT# 2 MATERIALS: - One sterile agar plate - A culture of Escherichia coli bacteria - A sterile swab - One tetracycline antibiotic disc - One penicillinG antibiotic disc - Forceps EXPERIMENT# 2 PROCEDURE (FIRST WEEK) 1: Get one agar plate and label it on the bottom with your name and the date. Take a swab and soak it into the liquid bacterial culture. Open the cover of the plate and gently streak the swab numerous times across the agar so that bacteria will grow on the whole plate. Use forceps to remove an antibiotic disc and place it on one side of the plate (approximately 1/2 inch from the side). On the opposite side place the second antibiotic disc. 2: Cover the plate as soon as you placed your antibiotic discs on them. Your plate will be incubated at 37C so that the Escherichia coli bacteria can grow on the plate. EXPERIMENT# 2 PROCEDURE (SECOND WEEK) 1: Record what you observed on the plate 2: Give an explanation for why you did or did not see growth on around the discs.