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An investigation into the antibiotic effects of penicillin and streptomycin on the bacterium Escherichia coli

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Risk Assessment: Risks related to substances, apparatus or procedures Precautions to be taken Contamination of microbes: To prevent this, it will be important to follow sterile techniques throughout. I will be wearing gloves at all times during the handling of the microbes. I will also take utmost care when handling the cultures that I do not drop them, as this could easily cause them to spread if the container being used, were to break open. For example, the microbes could spread aerobically. It would also be a good idea to work near a Bunsen burner at all times so that an updraft of air is created, causing constant airflow and therefore less chance of unwanted pathogens from settling in the microbial cultures. An investigation into the antibiotic effects of penicillin and streptomycin on the bacterium Escherichia coli. Aim: To plan an investigation into the antibiotic effects of penicillin and streptomycin on the behaviour of the bacterium E. coli. Introduction: I will be carrying out this experiment to find out which antibiotic (penicillin G or Streptomycin) is more effective at killing the bacterium E. coli. This information could be useful to a number of people, but an investigation of this nature would prove most useful to members within the medical profession. This is due to the fact that it would enable them to treat patients with more knowledge and understanding of the bacteria and antibiotics being discussed. Essentially, there are three general types of bacteria, each being specialised to different environments and having specific advantages in various organisms in relation to other forms. ...read more.


coli. (3) Pour plates are usually the method of choice for counting the number of colony-forming bacteria in fluids, as they give a very even distribution of the bacteria being used; this allows the measurement of the area killed off at the end of the incubation to be measured more easily and accurately. Their preparation is, however, time consuming. Other disadvantages are the reduced growth rate of obligate aerobes in the depth of the agar and the danger of killing heat sensitive organisms with the hot agar. When preparing a pour plate, you have to mix all the bacteria into molten agar, which causes there to be bacteria at all depths of the agar, when it would be more desirable for the bacteria to be solely on the surface. This could be sorted out by pouring the molten agar containing the bacteria to a depth of just 1 or 2mm in the Petri dish. These disadvantages cannot be raised against the streak plate method, as it is easier to perform; only it gives less reliable results. But due to the nature of the preparation for it, it would be a much harder method to measure the final outcome. For the above reasons I have decided to perform the pour plate method in my investigation, as I want to obtain the most accurate results possible. Key factors to take into account 1. Temperature to incubate at. 2. Period of time left to leave for and frequency of times to view it. ...read more.


3. The following step should be done under sterile conditions to avoid contamination, it should also be done as fast as possible to prevent any unwanted pathogens from entering the cultures. 4. Sterilise a wire loop by flaming it until it goes red. 5. Remove the lid from the bottle containing the E. coli, then flame the rim of the bottle to sterilise. 6. Then remove the lid from the bottle containing the liquid, and flame the mouth. Then with the sterile wire loop, transfer one scoop of the E. coli culture into the liquid agar, dipping the loop in fully, so as to properly mix it in. 7. Then immediately pour the liquid agar containing the E. coli into a warm (to prevent water condensing on the lid as I pour), sterile Petri dish by only lifting the lid just enough to pour it in, therefore preventing contamination. 8. Then replace the lid, and make sure that the culture is evenly distributed and flat throughout. 9. Once the agar has hardened, place 2 discs of filter paper on the surface, one which has been soaked in penicillin G and dried, the other, soaked in streptomycin and allowed to dry. The two discs should then be transferred using sterile forceps for each. 10. Place the control disc at equal distances from the other two discs, on the surface of the agar using sterile forceps. 11. Then secure the lid of the Petri dish with sellotape, and then turn it upside down to prevent condensation forming on the lid whilst it is being incubated. 12. Leave the culture in the incubator for 5 days, at a temperature of 30�C. ...read more.

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