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Biology SNAB Core Practical - Gram Staining Bacteria

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Core Practical - Gram Staining Bacteria Introduction When a bacterial infection is diagnosed antibiotics may be prescribed. Different antibiotics are not equally effective against all bacteria, so the correct antibiotic must be selected for a particular bacterial infection. In some cases the most effective antibiotic is known, but in other cases tests need to be carried out by a pathology department. In this activity I will be testing the effectiveness of several types of antibiotics on bacteria Hypothesis The aim of the experiment is to test the effectiveness of different types of antibiotic on bacteria. The bacteria that we will be using will be Escherichia Coli and Bacillus Subtilis. I predict that the antibiotics will be more effective on B. Subtilis. Variables The Independent variable in this investigation is the presence of the different types of antibiotics. This will be changed by using a mast ring which has all the different types of antibiotics around it. The Dependant variable in this investigation is the zone of inhibition around the disc. This will be measured by measuring the zone around the disc, using a ruler, after the Petri dish had been left for an adequate amount of time. ...read more.


5) After incubation, observe and measure the clear zones around the antibiotic - the zone of inhibition. Risk Assessment Likelihood and Severity is on a scale of 1-5, one being low, five being high. Risk is calculated by multiplying likelihood and severity, so is out of 25. Generally, if the risk is over 10 then the experiment should not take place. Validity The results will be valid because the experiment is designed to test the hypothesis, so the experiment will test what it is intended to. The results may not be that reliable as we are not doing any repetitions. The results should be accurate as the equipment is all functioning correctly currently. Results E. Coli B. Subtilis S. Albus Antibiotic Zone(mm Antibiotic Zone(mm) Antibiotic Zone(mm) PG 0 PG 0 PG 14 NO 21 NO 13 NO 15 OX 0 OX 17 OX 25 FC 0 FC 21 FC 20 T 23 T 20 T 21 E 12 E 18 E 16 C 18 C 16 C 19 S 21 S 13 S 12 Zone = Zone of Inhibition (clear area around antibiotic) ...read more.


Next, some of the zones were not circular in shape, and therefore had sides that were longer than others. This could create different results depending on the angle at which you measure the zone of inhibition. To get around this I would make it clear at the start to measure the longest diameter of the zone, so as to get consistent results. A random error may have occurred for E. Coli at the antibiotic Ethylronyin as the reading is significantly lower Different amounts of agar jelly may also have been used, which could produce different results, as this is the medium for the bacteria. Therefore in future I would say that we shouls use a set amound to agar. The same could be said for the bacteria as the amount added was just 'a pipette'. I think that the results were valid, as they tested the hypothesis. I don't think that the results are very reliable, as we did not do any repetitions, however I think that the results were accurate due to the simplicity of the method and equipment. If I was to take this investigation further, I would test more bacteria against more types of antibiotics. ...read more.

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