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Unit 6c applied science DISTINCTION
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This assignment got me a distinction, it is very easy to understand and will give you a distinction also, so use it as a reference. Message me if you need anymore help!
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Unit 6c assignmentAbstract
In this paper I addressed the issues facing bacteria and how antibiotics affect on the certain
bacteria. It is important since millions of people a day take antibiotics in order for the
bacterial infection to go away so they can regain their health. However, some bacteria are
becoming super bugs where they gain resistance to these antibiotics so it becoming
increasing difficult to treat them that’s why this research is crucial. The method which I used
was the Kirby- bauer method which is commonly called disk diffusion test. I did this in order
to gain zones of inhibitions. The findings I got was not what I hypothesised and were
surprising because ampicillin did not form a zone of inhibition however, Cefoxitin formed the
largest zone of inhibition. I conclude based on these findings that my experiment is
unreliable and would need to be performed again to gain accurate results. The broader
implications of these research is to stop super bugs from forming but knowing why they
form in the first place. The limitations for my results were that it can vary in results from
person to person because it’s an observational experiment and smaller zones of inhibition
are sometimes overlooked and this can impact the results greatly.
Hypothesis:
With extensive knowledge in this investigation due to my previous assignment I can
hypothesise that ampicillin would be the most effective antibiotic at killing E. coli since it is
the most potent antibiotic to this bacterium. I would also hypothesise that for Bacillus
megaterium the most effect bacteria would erythromycin because in previous trails it has
shown to be effective at killing this bacterium.
Method
Previous method:
1. Label 2 petri dishes which have the same dimensions as A and B
2. Write down the day and time onto the petri dishes so it can be used for later
3. Use sterile forceps to place the mast ring/ paper discs of distilled water into the
correct agar plate (one for each bacterium)
4. Close each petri dish but make sure that a small gap is left so that oxygen can enter
so there is no build-up of anaerobic bacterium.
5. Leave the agar plates to incubate at a temperature of 25 Celsius for approximately 24
hours
6. Open each agar plate and use a ruler to work out the zone of inhibition for each mass
ring section.
New method:
1. Wipe down all the surfaces using a disinfectant to stop contamination
2. Next, they would wipe down the surfaces until it is dry
, 3. After that they would begin to set up the Bunsen burner. They would do this by
placing a heatproof mat under the Bunsen burner and then attach the gas and light it
after you turn on the gas
4. Next set the Bunsen burner to a yellow flame since it is not in use
5. Next, they would take the bacteria from outside the container and place it on the
desk to make it easier for later but do not open it
6. After that set the Bunsen burner to a blue flame
7. Next get the bacteria smearer and squirt ethanol onto it (5-10ml)
8. Then place it onto the flame for 5 seconds
9. Take out of flame and place onto the disinfected side
10. After that get the bacteria strain bottle and take the cap of and flame the inside of
the bottle/tube to disinfect it (maximum 4 seconds)
11. Then place the bacteria bottles cap on and place on the side for later use
12. Now by using a sterilised syringe open the bacteria bottle and get the bacteria into
the syringe only between 0.10ml-0.20ml
13. Place the cap on the bacteria bottle
14. Then open the agar plate and empty the contents of the syringe into the agar plate
15. Continuously after grabbing the smear, smear the contents of the bacteria into the
agar by using a circular motion
16. Place the lid on the agar plate and cellotaph on it to let a little air in so it doesn’t
crease harmful aerobic bacteria
17. Label the agar plate by writing the bacteria in question, volume used, time of the
experiment and day of the experiment and finally their name
18. Repeat the experiment from steps 7- 17 for how many bacteria they are
investigating (2)
Changes made:
o Wiped down the surfaces before and after each experiment
I made this addition to further reduce the risk to contamination in my experiment which would
Improve the reliability of my experiment since there is no chance of the bacteria or equipment being
contaminated due to the surfaces being disinfected.
o Flamed the inside of the bacteria tube
I made this addition towards my investigation to reduce the risk of contamination towards my agar
plate and to reduce the exposure of oxygen to my bacteria, so the results are as reliable as possible.
o Used ethanol on the smear to disinfect it instead of putting it directly on the Bunsen
burner
I used ethanol on the bacteria smear so the smear can get evenly disinfected without the risk of
damage towards the equipment.
Preliminary results:
I could not get results for my preliminary work since I did not put antibiotic tabs on the agar plate so
the zones of inhibitions around them could not form. However, I managed to get good results and
learnt a lot to improve the safety and improve the results of the experiment with the help of the lab
technician showing me how to properly perform it. From my agar plates I managed to get good
lawns. -->
, Final results:
E. coli
CXT PEN STR SFZ TET AMP CHC ERY
(mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm)
B1 11 N/A 11 N/A N/A N/A 10 N/A
B2 11 N/A 10 N/A N/A N/A N/A 5
B3 10 N/A 13 N/A 3 N/A 13 N/A
Bacillus megaterium
Sample CXT PEN STR SFZ TET AMP CHC ERY
(mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm)
A1 N/A N/A N/A N/A N/A N/A N/A N/A
A2 N/A N/A N/A N/A N/A N/A N/A N/A
A3 N/A N/A N/A N/A N/A N/A N/A N/A
These results are invalid due to a possible contamination in the experiment, so no clear zones of
inhibitions formed.
I have used 1 decimal place for my recording since I used a standard 15cm ruler using one decimal
place is the most appropriate since I could record it accurately however, if I used more than one
decimal place it would be pointless since it would be a complete guess since I’m using the naked eye
and can't see to that range.
Graphs:
This is the table which represents the agar plate of b1 on my investigation and it shows the zone of
inhibition sizes when comparing them to different antibiotics against E coli. It also shows that I
managed to gather clear zones of inhibitions for the following antibiotics against E coli; cefoxitin,
chloramphenicol and streptomycin. It also shows which antibiotics didn’t make zones of inhibitions
which are; Ampicillin, Erythromycin, Tetracycline, Sulphafurazole and Penicillin.
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