*The agar plates now need to be sealed; to do this use cellotape and stick it on to the lid and over the side in a crossed position (look at diagram ‘B’), and left in a controlled environment. This should be stored for 48 hours at just over room temperature. However if this is not possible then they need to be stored for a longer period of time at room temperature. If this is done however the results may not be as good as they could be.
*At the end of the incubation period you can now need to record your results you do this by measuring the inhabitation zone and take away the size of the cork borer. You can turn the agar plates upside down to look at the results now, as all of the substances will have dispersed in to the agar jelly. Do not open the plates as this will release the bacteria and it could be very harmful.
Fair test: ~
To make this experiment a fair test you must: ~
*Sterilise ALL of the equipment. If some of it is un-sterilised then the bacteria on this item may affect the experiment as it may get onto the agar jelly.
*Use the same sterilised cork borer to do all of your holes. This make sit a fair test as then the holes where the substances goes are the same size so they start with the same boundaries. It also means that you can take the exact measurement for each hole, as this needs to be subtracted from the result.
*Put in the same amount of substances in each hole. If this is not done then there may be more liquid in one hole than the other and this will affect the results.
Results: ~
Class results: ~
My results: ~
Look at diagram ‘C’ and ‘D’
Analysis: ~
My results show me that the higher the concentrate of bleach the more bacteria was killed. I predicted that this would happen, and the results now reinforce my prediction. However it is difficult to see any particular pattern in the class results of the different substances. We can see that Dettol was the strongest, so the best at killing Microcuccul luteus. On the other hand we can see that water and Listerine were the weakest, so the worst at killing Microcuccul luteus.
Conclusion: ~
The reason that we knew that Microcuccul luteus was produced was because you could see small round dots on the agar jelly. Because of this you were then able to find the inhabitation zone. This is when the bacteria have been killed and there is now a clear zone. There was no inhabitation zone around the water sample because it did not contain any anti microbial agents. It was just pure tap water so did not kill any of the Microcuccul luteus. If bacteria had not been distributed across the agar jelly then you would not have been able to see the diffusion of the bleach and you would not be able to see the inhabitation zone. This is because the bleach has to kill the visible bacteria for you to see the reaction that has accrued. If there were no bacteria present then there would be no visible results. The size of the inhabitation zone is relative to the strength of the product. The stronger the substance, the larger the inhabitation zones thus the better at killing bacteria. The most anti-microbial activity that has taken place is with the Dettol substance. It had the largest inhabitation zone with my results, and the class results. The anti-microbial activity was larger in relation to the higher concentration of bleach. This was the same for the whole class. A bleach manufacturer could use the results to let his customers know how effective bleach is at killing bacteria. He could tell them how each concentration worked. It would be possible for the smallest concentration of bleach to kill a small amount of bacteria. This would be useful if customers needed the bleach to last for a long time; if they were cleaning a large area.
Evaluation: ~
Some of the results that were obtained I was quite surprised with. I predicted that the 20% bleach concentration would have the best anti-microbial activity however this was not true. I also predicted that toothpaste would have a large inhibition zone, however the inhabitation zone was small which was the opposite of what I predicted. I predicted that water would have the worst inhabitation zone. This is because water does not contain any anti-microbial agent so it is unable to kill the Microcuccul luteus.
There was a high chance of errors occurring during the experiment. These consisted of:~
Distribution of the Microcuccul luteus.
Thickness of agar
Diameter of cork borers
Volume of agent
Measurement of diameters
Judging of the edge of exclusion zones
The distribution of the Microcuccul luteus, could quiet easily differed in each plate. for instance one of the plates used in the experiment may of contained more than another plate. This would effect the results because the anti-microbial agent would have to work harder to kill of the bacteria.
If the agar jelly had been of different thickness in each of the agar plates, then the experiment would be faulty due to the anti-microbial agents not effecting the bacteria as well as they should do.
Due to cork borers being different sizes, this effects the results. To make it a fair test all of the cork borers used must be the same size. If not there will be anti-microbial agent it that hole.
To make this experiment fairer every agent would have to have the exact same volume. If they all have different volumes then they will effect the results. This is due to the fact that there will be more of one compared to the other.
When measuring the diameters of the inhabitation zones people may perceive it very differently. For instance one person may think that a measurement is closer to on half i.e. if 4.5mm they may perceive it as 5mm. This will effect the results because all were taken in mm, so a good eye is needed to get an exact measurement.
People will judge the outside of the exclusion zones differently. To make it a fair test you would only put one anti-microbial agent in an agar plate. This would mean that it is easy to see the inhabitation zone thus resulting to easier measurements.
You could extend this experiment by using a wider variety of anti-microbial agents. not only could you use household products, you could you industrial products and see what results you would get using them. You would then be able to compare the results and see what type of products work better. You could also find a list of the most popular household products and test theses against each other. This would be helpful for people interested in buying products that kill a wide range of bacteria and they could see what works best.
Another experiment that you could do to test the effectiveness of anti-microbial agents is to get a test area, for instance a kitchen floor. You would then be able to clean parts of his floor with different agents. You would take a swap of the area before and after cleaning it and see what product worked the best.
