The Effectiveness of Garlic on
Bacterial Growth
By Juliana Guarino
Purpose
• To test whether garlic and or garlic extract will have
an effect on the growth of E. coli.
• Its been said that many herbs and spices, garlic
specifically, can be used for antibacterial purposes.
Background Information
• Garlic was used medicinally dating back to the
Neolithic Age
• It was used for protection against the Great
Plague of London in 1665 and also during
World War I
• Recent studies confirm that garlic is effective
in inhibiting the growth of different bacteria,
fungi and viruses
• The antibacterial properties are due to the
allicin,C6H10OS2, that garlic contains. It
stimulates the immune system by increasing
the number of white blood cells called
lymphocytes.
• If crushed or finely chopped, more allicin is produced
• If cooked under high temperatures, the effectiveness of
the allicin will decrease.
Hypothesis
• All forms of garlic used will inhibit bacterial growth
– The solution containing fresh, mashed garlic and sterile
water will be the most effective in doing so
– The solution comprised of cooked, mashed garlic and
sterile water will be the least effective
Procedure
1. 1.0g garlic powder and 10.0mL sterile water were
combined and filtered into a small, sterile jar. This was
specimen A.
2. One clove of fresh garlic was mashed to a pulp and
combined with 10.0mL sterile water. It was then filtered
into a small, sterile jar, creating specimen B.
3. Two sterile pipettes were used to extract 10.0 mL of
organic garlic extract and 10.0mL of sterile water in a
small, sterile jar. This was specimen C.
4. To create specimen D, 50.0mL of tap water was boiled in
a beaker on a hot plate. Once boiling, one clove of garlic
was put in the water for two minutes. The garlic was then
removed and crushed with with 10.0mL sterile water and
filtered into a small, sterile jar.
5. Specimen E consisted of the control, 10.0mL sterile water.
6. The five jars containing the solutions were then
autoclaved to prevent mold growth.
7. They were poured into five Petri dishes and labeled A-E.
8. Five blank discs were submerged into each Petri dish.
9. The bacteria, E. coli, was hydrated and then evenly
streaked onto five different agar dishes using sterile
technique.
10. Using sterile tweezers, one blank disc from each solution
was added onto each of the five dishes.
11. The agar dishes were labeled 1-5 and taped shut. They
were put in the incubator at 37oC.
Results and Data
Zones of Inhibition (mm)
Trial 1
A: Garlic
Powder
B: Fresh Garlic
C: Garlic
Extract
D: Cooked
Garlic
E: Sterile Water
0
0
0
11
0
Trial 2
12
Trial 3
12
Trial 4
13
Trial 5
13
Average
12.2
Results and Data
The Effectiveness of Garlic in Fighting Bacteria
Average Zones of Inhibition (mm)
14
12
A- Garlic Powder
B- Fresh Garlic
C- garlic extract
D- cooked garlic
E- sterile water
10
8
6
4
2
0
A
B
C
D
Different Solutions
E
This graph shows the zones of inhibition produced from adding
different forms of garlic to E.coli
Notice that only solution D, cooked garlic, produced zones of
inhibition.
This suggests that cooked garlic is the only form of garlic that inhibits
bacterial growth
Discussion
• Factors that could have affected results:
– Garlic solutions were not concentrated enough
– Autoclaving the solutions could have made the allicin
ineffective, similar to cooking.
– The garlic not being used immediately could have
weakened the allicin
– Not enough samples of fresh garlic
• Further Studies:
– Use other forms of bacteria
– Using an alternate heating method such as baking
– Test in different temperatures
Discussion
• First set of trials produced excessive mold growth, results
were inconclusive
• To prevent this the solutions were autoclaved the second
time
Conclusion
• Cooked garlic was the only solution to produce zones
of inhibition
• Hypothesis was rejected
• Results are important to the world because it means
that cooked garlic can be used for certain
antibacterial purposes.
References
• Bacteria. (2010). In JRank Science Encyclopedia . Retrieved
from http://science.jrank.org/pages/714/Bacteria.html
• Clark, M. (2005-2010). E. coli. Retrieved from
http://www.about-ecoli.com/
• Dolby, V. (1999, July). Garlic: Strengthens our immunity,
improves infection-fighting ability. MoneyWatch, better
nutrition. Retrieved from
http://findarticles.com/p/articles/mi_m0FKA/is_n6_v58/ai
_18356463/
• Medham, T. (2003-2008). Garlic central. Retrieved from
http://www.garlic-central.com/antibiotic.html
• Sterile technique. (n.d.). Retrieved from
http://www.umsl.edu/~microbes/techniques.html
• Are there any questions?