The effects of Garlic and Mint on bacteria

Garlic and mint

Introduction

I am going to be trying to find out whether garlic has stronger antibacterial properties than mint. Mint has always been used in toothpaste and I will be trying to find out whether this is just because of the fresh breath it leaves you with or, because of its antibacterial properties. If garlic has stronger antibacterial properties why not put garlic in toothpaste?

Plants have always been susceptible to infection by bacteria and fungi. The plants do everything they can to repel such attacks and it is known that several plants have antibacterial properties that could help humans. The cells the plant produce are either toxic to the bacteria or interfere with the bacteria’s metabolism in some way. When you clean your teeth you can feel the mint numbing your mouth and gums, this obviously has some effect on bacteria, but would garlic be more effective?

Hypothesis

I think that garlic will have a greater antibacterial effect than mint. This is because garlic has a stronger flavour and is known to repel some larger organisms like mosquitoes. I think garlic will have a greater antibacterial effect than mint.

Plan

I plan to make a culture of bacteria on an agar plate. I will make two different cultures, one will be E.coli (Escherichia coli) this is a gram-negative bacteria. The other bacterium I will use is Bacillus subtilis this is a gram-positive bacteria. I will make one culture of each. In the culture of E.coli I will put a sample of mint, garlic, alcohol and distilled water using small discs of impregnated filter paper. In the second culture I will use a cork borer to make four holes in the agar and then pipette a small amount of garlic, mint, alcohol and distilled water into each hole.

Equipment / materials

15 cm3 of sterile agar in an agar bottle or test tube: This is to put into the petri dish to create suitable nutrients for my bacteria cultures to grow.
Sterile petri dish: to put the agar in and to grow the bacteria culture in.
1cm3 sterile pipette: to pipette the bacteria into the petri dish.
Plant material: (mint and garlic cloves) to perform experiment on
Pestle and mortar: to crush the mint and garlic
10cm3 industrial methylated spirits: to sterilise the lab equipment.
Paper discs: to soak in the mint and garlic ...

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Equipment / materials

15 cm3 of sterile agar in an agar bottle or test tube: This is to put into the petri dish to create suitable nutrients for my bacteria cultures to grow.
Sterile petri dish: to put the agar in and to grow the bacteria culture in.
1cm3 sterile pipette: to pipette the bacteria into the petri dish.
Plant material: (mint and garlic cloves) to perform experiment on
Pestle and mortar: to crush the mint and garlic
10cm3 industrial methylated spirits: to sterilise the lab equipment.
Paper discs: to soak in the mint and garlic and place in the bacteria culture.
Sterile forceps: to pick up the paper discs and make sure they don’t touch anything else.
Tape: to tape the petri dish shut once they are ready to incubate.
Marker pen: to mark on the petri dish’s which bacteria they are and which plant under test is which.
Incubator set at 25C: to incubate the bacteria and give it good growing conditions.

Possible risks

Methylated spirits are highly flammable and toxic, so we must be careful to keep the container of methylated spirits away from the Bunsen flame. And wear gloves during the experiment.

Live bacteria are being used so there is a possible health risk during this experiment. We must use the aseptic technique. To do this we will need to sterilise the bench we are working on and have a Bunsen burner set to a blue flame on at all times. Whenever we use a piece of equipment it has to be sterile, if its not already we will have to dip it in the methylated spirits and then put it into the Bunsen flame to sterilise it. When the bacteria pot is open we will flame the neck of the pot and be careful not to put the lid down anywhere. We will then take what bacteria needed, re-flame the neck of the bottle and replace the lid. After we have completed the experiment the bench should be sterilised again. This will prevent any bacterial contamination.

All used petri dishes have to be autoclaved to avoid environmental contamination.

There are not many ethnical problems with this experiment because the use of bacteria is considered acceptable.

Method

First we will have to make the bacteria culture. To do this we will have to collect a bottle or test tube containing 15 cm3 of sterile nutrient agar, place the tube into hot water to melt the agar (agar melts at 97 degree C), allowing air to escape. Once the agar has melted remove the tube from the water with a cloth and let it cool to about 50 degrees C. Once it has reached this temperature it should be ok to handle. Pour the agar into the petri dish and allow it to set. Once set, seed the agar plates with the appropriate bacteria. Now we will obtain garlic and mint extract by crushing 3g of the plant in a pestle and mortar and add 10cm3 of industrial methylated spirits. This is used rather than water because it will kill any bacteria that may be in the extract. Pipette 0.1 cm3 of this extract onto a sterile paper disc, place the disc on the agar plate. Repeat this 4 times with mint, garlic, alcohol and distilled water.

Results

From these results I was able to plot these graphs:

This graph clearly shows that mint is the most effective sample at killing Bacillus subtilis.

From this graph it is clear that garlic is the most effective sample against E.coli.

Analysis

These results show that mint has a stronger affect than garlic on bacillus subtilis, making an average inhibition zone of 130.1 mm. Garlic on the other hand only made an average inhibition zone of 125.1 mm. This does not support my hypothesis because I thought that garlic would have a greater effect on both bacteria. The Chemicals in mint cells are more toxic to bacillus subtilis than the chemicals in garlic cells, therefore mint would be more effective in controlling this bacteria.

E.coli on the other hand was effected more by garlic, having an inhibition zone of 131.4 mm, where as mint only had an inhibition zone of 119.1 mm. This supports my hypothesis because I thought garlic would have a greater effect due to its effect on insects. This is because the chemical in garlic is more toxic to E.coli than the chemical in mint. In this case garlic would be more effective to have in toothpaste.

I think my results are reasonably reliable because I repeated each experiment 4 times and took the mean average, however some of the results are quite far spread. This suggests that my results aren’t 100% reliable. There will be a small amount of human error due to measuring the inhibition zones. My results were similar to other students in the class. This supports my statement that my results are reasonably reliable. There are no major anomalies in my results therefore I was able to include all my results in calculating the mean.

My results are reasonably accurate. If I had more time I would like to have tested more samples to increase the reliability. I would also have used a more accurate measuring instrument to measure the inhibition zone, removing human error.

So my over all conclusion is that mint is most effective at killing bacillus subtilis and garlic is most effective at killing E.coli.