Cpac 9: Antimicrobial Properties Of Plants

Question 1

Method: stage 1

Answer 1

1. Prepare a sterile Petri dish with some sterile nutrient agar.
2. Add a culture of a known, single strain bacteria evenly to the surface of the agar using a spreader and a pipette. Allow time to dry.

Question 2

Method: stage 2

Answer 2

3. Obtain a plant extract by crushing 3 grams of a plant with 10cm^3 of ethanol.
4. Pipette 0.1cm^3 of the extract onto a sterile filter paper disk. Let this paper dry then place it onto the agar.
5. Prepare control discs by adding ethanol to the paper disc, letting it dry, then placing it into the agar using tweezers.
   6.First repeat this 5 times, after that repeat with different plants.
6. Incubate the plate at 25°c (not 37°c so no harmful bacteria develops).

Question 3

Method: stage 3 (a week later)

Answer 3

7. Measure the diameter of the zone of inhibition at several points around the disc and take a mean average.
   8, compare this against the control dish.

Question 4

Conclusion/analysis: (LONG)

Answer 4

The mint and oil appear to have antimicrobial properties, despite no evidence that they possess them. The menthol component of mint is a mild anaesthetic. The zone of inhibition for garlic was the greatest as garlic is proven to be a fairly strong, natural antibacterial. This is due to the active ingredient ‘allicin’ in garlic which interferes with the lipid synthesis and RNA production in bacteria. This inhibits growth and leads to the death of bacteria. However, there are some random zones of inhibition, one being in the control zone which is likely due to contamination of microbes due to random error. Therefore, improved aseptic techniques should be used (washing hands before and after with alcohol gel and more care taken when transporting the substances).

Question 5

Conclusion (SHORT)

Answer 5

The larger the zone of inhibition, the greater the anti microbial properties.