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Investigating the effect of two different antibiotics on bacterial growth

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Investigating the effect of two different antibiotics on bacterial growth Introduction Antibiotics are drugs that kill bacteria by inhibiting their growth and slowing down their rate of division. There are many different variations of antibiotics each one designed to kill bacteria which causes infection within the human body. In this investigation two unknown antibiotics will be used on ecoli bacteria, different concentrations of both antibiotics will be used to determine the effectiveness on the bacteria by assessing the size of the clear zone. Hypothesis: There will be no significant difference in the zone of inhibition by using known concentrations of unknown antibiotics on the agar plate. The dependent variable that will be measured in the experiment will be the size of the clear zone in mm and the independent variable will be the different concentrations of antibiotics and the type of antibiotic due to testing the growth of bacterial growth with two unknown antibiotics. Apparatus * 2 petri dishes * 2 bottles (Molten agar and bacterial culture) * 3 syringes 5ml x2 and 10ml x1 * 4 medium sized bottles * 8 Sterile paper discs * 2 unknown antibiotics * Bunsen Burner * Pure water * Heat proof mat * Tweezers * Marker Pen * Scissors * Sellotape * Cleaning cloth * Disinfectant spray * Incubator set at ...read more.


Lab coats and goggles were worn to prevent contamination from our clothing and our hands were washed before and after the experiment ensuring our hands were free our bacteria. Results Clear zone diameter (mm) Student Number Antibiotic 1 (purple) concentration Antibiotic (Clear) 2 0 25 50 100 0 25 50 100 1 5 26 27 20 5 25 14 12 2 5 10 30 20 5 13 10 7 3 5 19 20 18 5 10 13 8 4 5 15 17 10 5 11 7 14 5 5 19 15 25 5 8 10 17 6 5 12 14 19 5 10 12 13 7 5 7 11 19 5 9 12 20 8 5 19 30 35 5 9 9 19 9 10 16 13 18 4 6 9 11 10 5 16.5 9 11 5 9 11 8 11 5 7 22 10 5 8 8 13 12 5 19 33 41 5 11 13 9 13 5 15 23 12 5 10 15 16 14 5 12 11.5 13 8 10.5 11.5 10 15 5 17 15 12 10 15 8 20 16 5 20 14 15 6 18 12 15 17 5 26 15 30 8 5 9 10 18 5 13 19 25 5 9 12 14 19 5 11 21 18 12 ...read more.


Furthermore, there can be human error when measuring the size of the clear zone using a ruler, this will lead to different results being recorded. Another limitation is contamination, slight opening and closing of the petri dishes to place the paper disc on the agar plate. Whilst opening the petri dishes microbes in the air may enter into the nutrient rich petri dish which could affect the effectiveness of the antibiotic in preventing the growth of the bacteria, which will lead to different clear zones being produced therefore affecting the results which could lead to a different conclusion at which concentration and which antibiotic is most effective at killing the bacteria. Improvements The first improvement that should be made is doing repeats, the repeats will allow you to assess the validity of the results and spot anomalous results as the experiment was only carried out once. In-addition, instead of using a ruler to measure the inhibition zone a digital Vernier Caliper should be used which is more accurate than measuring with a ruler, therefore the results will be more precise and reliable, this will give a better indication into the effectiveness of different concentrations of antibiotics on the growth of bacteria. ...read more.

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