Antibacterial properties of plantsIntroduction:Anti-bacterials are substances that work by utilizing a component that destroys the bacteria in an area, often a surface for example. They interfere with the growth and reproduction of the bacteria which causes it to die out. Many plants have active ingredients that have anti-bacterial properties, but their effectiveness varies. This is what we shall investigate in this experiment. Garlic should have the best antibacterial properties as it is the most acidic, Hypothesis: Garlic will have the largest zone of inhibition of bacterial growth, and therefore the best antibacterial properties of all the tested plant types.Variables: Independent We will change the type of plant material that is tested for antibacterial properties.Dependant We will measure the zone of inhibition ring size surrounding the disks which have been dipped in the plant material.Validity:Control Variables: The size of the disks used, which links in with:

The amount of plant material solution on the disks and therefore agar.

Time left for solution to kill bacteria.

Strength and type of bacteria used.

The conditions in which the plates are left (Room Condition)

MethodObtain the plant extract solution by crushing 3g of the plant with 10cm of an alcohol solvent or methylated spirit in a pestle and mortar. (This kills bacteria, why we don't use water)

Now pour an agar plate, using hot agar from a water bath. The first step is to evenly pipette 1cm of bacterial broth into the plate.

Then using a sterilised petri dish and the aseptic technique for the bottle lid (heat top of bottle above a buncen burner for example), pour 15cm of agar into the dish. Note: As mentioned, the aseptic technique should be implemented throughout this experiment. The lid of the petri dish should only be open when necessary for quick periods of time; use sterile pipettes and bleach down the bench before you start.

Now using 3 separate sterile pipettes, release 1-2cm of each plant solution onto a 13mm assay disc. Use just the spirit on a 4th disk for a control.

Quickly place these in the petri dish in separate areas, a quarter each for example. Seal the lid with tape.

Culture the bacteria in the plates in a set environment an incubator at 25 degrees C.

Leave them for a set period of time and observe the zone of inhibition surrounding each disk. The largest zone killed the most bacteria.

Safety:The alcohol solvents and spirits are highly flammable so keep away from the buncen burners used for sterilisation. Use the aseptic technique to avoid contamination and also spreading of bacteria onto yourself/surroundings.Do not inhale or touch the agar plates with bacteria. This is dangerous.Results:Antibacterial Plant mixture typeZone of Inhibition (mm)

Our ResultsExpected

Mint0300

Garlic0706

Aloe Vera78.5380

Control00

Conclusion source of errors:One error was that the bacteria in some plates was visibly not evenly spread. This meant that some of the plant material would not have a chance to kill bacteria, or it was more concentrated in one area so it would be harder to clear.

Contamination could have caused unexpected/unwanted bacteria to grow. This could have grown anywhere in the dish, meaning some extracts might have more bacteria in their section.

Some disks could have absorbed more extract than others as the solutions would have different densities, absorbencies etc. For example the mint crushed much better than the garlic.

EvaluationTo improve on the first error - a good shake to evenly distribute the bacteria solves the problem to some extent.

To improve on the second error - The aseptic technique should be carried out properly and thoroughly to avoid this.

To improve on the third error - Use a more efficient way of crushing that pestle and mortar. Perhaps blending.