Natural vs. Synthetic Antibiotics: Which Works Better?

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Updated on Jan 17, 2014

Grade Level: Late Middle/Early High School; Type: Life Science


The purpose of this project is to test the efficacy of both synthetic and natural antibiotics. Cultures of benign bacteria will be grown in the presence of both a common antibiotic, and a natural chemical purported to be an antibiotic (garlic in this case, but anything can be substituted), and we will measure the inhibition of bacterial growth.

Research Questions:

  • What is an antibiotic? How does it work?
  • What is the ‘zone of inhibition’ in bacteria cultures?
  • What does it mean to ‘culture’ bacteria?
  • What is aseptic technique?
  • What is a natural antibiotic? What are some examples?
  • What does it mean for a bacterial strain to be ‘resistant’ to antibiotics?

We are accustomed to buying our medicines in tidy chemical pills from the drugstore or the pharmacy. Most pharmaceutical companies would have us believe that they invented a ‘miracle drug’, but this notion is largely false: the vast majority of drugs on the market were original discovered in nature. We simply learned how to synthesize them in a lab. Many people believe that the original medications- usually plant based- are healthier. While biology is a complex alchemy, we can test one aspect- do natural antibiotics works as effectively as synthetic ones? This project aims to test this notion.

  • Petri dishes, pre-filled with agar medium or including agar ‘on the side’.
  • Benign strain of e.coli
  • Antibiotic disks, both treated and blank (Note: the above three materials can be found using the weblinks in the bibliography.)
  • Garlic ( or other natural antibiotic)
  • Metric Ruler
  • Incubation chamber (only if available- a warm, dark drawer will do just fine, it will just take an extra day or so)
  • Tweezers
  • Rubbing alcohol
  • Tape and markers for labeling

Experimental Procedure

  1. Purchase all materials. The only one to be careful about, in terms of timing, is the e.coli culture, although as long as it gets into the refrigerator shortly after arriving, you should be fine. Chose whatever antibiotic sounds interesting, but NOT PENICILLIN (too many bacterial strains are resistant!)
  2. If you are using Petri dishes and agar ‘on-the side’, you will need to prepare your Petri dishes. You can simply melt the agar in the dishes in the microwave, or even on the stove- all kits will have instructions on how to do this.
  3. Place the Petri dishes in the refrigerator while you prepare your other materials.
  4. Crush several garlic cloves using a garlic press, and soak your blank disks in the juice. Allow for them to dry.
  5. Inoculate an equal amount of dishes for each treatment- perhaps 5 for your antibiotic and 5 for your garlic disks, using a sterile cotton swab.
  6. Place the disks squarely in the center of your Petri dish, using tweezers, and cover with provided lids.
  7. Label your Petri dishes on the outside and place in a dark warm place or an incubator.
  8. Check daily for growth. When enough of the dish is covered with bacterial colonies, or enough to see the Zone of Inhibition, you are ready to take data.
  9. Using a metric ruler, measure the diameter of the zone of inhibition on all your Petri dishes, and record your data.
  10. Making the assumption that the Zone is circular, use the equation for the area of a circle to convert your diameters. Determine the area in mm2.
  11. Average all the areas for both your synthetic antibiotic and your natural one. Graph the means in a bar graph.
  12. Don’t forget to take photographs for your project board!

Terms/Concepts: Antibiotic; Natural antibiotic; Zone of inhibition; Petri dish; Agar nutrient; E.coli; Area of a circle; Aseptic technique; Bacterial colony;Antibiotic resistance


Purchasing Supplies

Antibiotic disks, both with antibiotic and blank

Petri dishes with agar (20 count):

Benign laboratory strain of e.coli

Aseptic Technique

Preparing a bacterial culture (NOTE: while the fire part is cool, it isn’t used when you have sterile swabs, used in place of wire loops. The important part starts at 0:55)

Another instructional video

Zone of Inhibition photos

Shumit DasGupta has worked for OSHA, UMBS, and Pfizer as a contract researcher, is a ten year veteran in science education, and has taught students in the International Baccalaureate program in both Chicago and San Francisco. Four of his students have made it to states, and one to nationals- the year it was held in Hawaii- and he was sad he couldn't chaperon. He also loves snorkeling.

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