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Garlic and Bacteria Inhibition

based on 11 ratings
Author: Maxine Levaren

Does garlic keep vampires away? You can’t prove it scientifically, but many people do believe that garlic is good for what ails you — among other things it helps to ward off infection.

Emily Koch noticed that her mom, who eats garlic, has fewer colds than other family members, so she decided to see if the stories about garlic are true.

You can get a look at her project display in the figure.

Figure: Project display for “Garlic and bacteria inhibition.”

Hypothesis

I believe that garlic will inhibit the growth of the bacillus subtilis bacteria, but not as effectively as antibiotics and disinfectants.

Independent variables

Bacteria-inhibiting agents

Dependent variables

Amount of bacteria incubated

Controls

  • Bacteria used
  • Technique and time of incubation

Experimental groups

  • Penicillin
  • Streptomycin
  • Tetracycline
  • Glutaraldehyde
  • 5 percent phenol alcohol
  • Garlic

Materials

  • 30 petri dishes
  • Nutrient agar (a culture containing agar used to grow bacteria)
  • Sterile paper disks
  • Bacillus subtilis broth
  • Home-built incubator (a sealed box with a heat pad underneath)
  • Light box
  • Penicillin
  • Streptomycin
  • Tetracycline
  • Glutaraldehyde
  • 5 percent phenol alcohol
  • Fresh garlic extract

Procedures

  1. Divide petri dishes into six groups of five.
  2. With adult supervision, melt the agar medium.
  3. When liquid agar cools, pour an equal amount into each dish.
  4. Press 25 cloves of garlic to make garlic juice.
  5. Saturate one group of paper disks in the following:
    • Penicillin
    • Streptomycin
    • Tetracycline
    • Glutaraldehyde
    • 5 percent phenol alcohol
    • Fresh garlic extract
  6. Put all petri dishes into incubator. The temperature in the incubator is 35@dgs C (95@dgs F).
  7. After 24 hours, observe petri dishes, and use light box to take pictures of each dish. Repeat again after 24 hours.
  8. Calculate zones of inhibition (the areas where no bacteria grow) to determine the area where each agent inhibited bacterial growth.

Results

The table shows the results for this experiment. The zone of incubation was calculated by placing the photograph of the petri dish on a sheet of graph paper, counting the number of squares with bacteria, and then calculating the percentage of squares where bacteria was inhibited from incubating.

Table                       Zone of Inhibition for Each Inhibiting Agent

Bacteria Inhibitor

Average Zone of Inhibition

Penicillin

22.14

Streptomycin

67.84

Tetracycline

65.30

Glutaraldehyde

18.09

5 percent phenol alcohol

14.94

Garlic

42.68

Conclusions

My hypothesis was that garlic would inhibit the growth of bacillus subtilis, but not as effectively as antibiotics and disinfectants. This hypothesis was partially correct; the garlic was effective. It incubated more bacteria than the antibiotics, but less bacteria than the disinfectants.

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