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Acne medication and bacteria Featured science projectScience project video


The materials required for this  science fair project are:

-    3  Petri dishes prepared with agar
-    1 disinfected swab
-    1 bottle of disinfected water
-    A piece of filter paper
-    A hole puncher
-    4 test tubes
-    1 measuring cylinder
-    1 pippette with disposable tips
-    Tetracycline
-    Clindamycin
-    Benzoyl peroxide (a pharmacist will be able to supply you with all 3 types of medication)
-    1 beaker of water
-    P. acne bacteria culture - check with your laboratory
-    1 forcep
-    1 digital weighing scale
-    1 marker pen


1.    The independent variable of this science fair project is the type of acne medication used - Tetracycline, Clindamycin and Benzoyl peroxide. The dependent variable is the size of  the inhibition zone (the area free of bacteria). This is determined by measuring the diameter of the area using a ruler. The constants (control variables) are the room temperature, the concentration of the medication and the ingredients in the Petri dish .

2.    Three Petri dishes are prepared using the agar and stored in the refrigerator. The Petri dishes are brought to room temperature before the start of experiment by removing them from the refrigerator. . The Petri dishes are labeled with the names of the acne medicationsTetracycline, Clindamycin and Benzoyl peroxide.

3.    Using the pippette, mix the respective acne medications with water and label them accordingly:
a.    Marked Tetracycline -  5mg of Tetracycline is mixed with 10ml water
b.    Marked Clindamycin - 5mg of Clindamycin is mixed with 10ml water
c.    Marked Benzoyl peroxide -  5mg of Benzoyl peroxide is mixed with 10ml water

Use 3 of the test tubes to contain each sample of diluted medication.

4.    Mix the fourth test tube containing 10ml of P. acne bacterium with 40ml of water. The swab is washed with disinfected water and dipped into the test tube containing the bacteria before gently swabbed all over the agar surface of the 3 Petri dishes. Ensure that you swab in at least 3 directions to cover the entire surface of the dishes.

5.    Using the hole puncher, punch out circular discs of filter paper . Pick up the filter paper discs using the sterile forceps and dip it  into the test tubes containing the acne medications. The discs are then placed in the center of the correctly labeled Petri dish. Close the cover of the dish. The Petri dishes are kept in a cool,  shaded place for the next four days for the bacteria to grow.

6.    4 days later, there will be a circular area around the filter paper  called the inhibition zone where there is  no bacterial growth. The diameter of this area is measured and recorded in the table provided below. The term "inhibition zone" comes from the Kirby-Bauer disk diffusion method. This method is used by microbiologists to assess the effectiveness of antimicrobial agents. As the antibacterial agent diffuses out from the filter paper into the agar, there will be a higher concentration of antibacterial agent nearer the disk. This concentration decreases gradually, as the distance from the edge of the disc increases. As long as the concentration of d antibacterial agent at any given distance is high enough to properly act as an antibacterial agent, no bacteria will grow at that location. Hence, if the bacteria has increased resistance, a smaller inhibition zone will be seen, and vice versa.

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Complexity level:
Project cost ($):
Time required:
1 day for preparation, 4 days for the science project experiment
Material availability:
Access to laboratory equipment (eg. petri dishes)
Safety concerns:

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.