Dry Heat Sterilisation Lab Report

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In Part A of the experiment which is sterilisation technique, three types of technique is used. The first technique is dry-heat sterilisation. Dry heat sterilisation takes a long time and is done at a high temperature of about 160°C for 60 minutes. In dry-heat sterilisation, there is two parts which are heating and flaming. Heating is when the inoculating loop and the needle are burned in the direct flame until it turns red in colour while flaming is just passing the forceps and mouth of the culture tubes through the flame to prevent bacteria from entering. The second technique is moist heat sterilisation whereby an autoclave is used. Autoclave is operated at a temperature of 121°C and a pressure of 15 psi for about 15-20 minutes. In this experiment,…show more content…
The first method is broth culture. In broth culture, Escherichia coli are grown in a liquid medium. It is shown that the nutrient broth appeared to have sediment. This shows that Escherichia coli carries out anaerobic and aerobic respiration as it can survive anywhere in the broth. The second method is agar slope culture where Escherichia coli are grown on a slant agar in a test tube. Escherichia coli are transferred into the medium through an inoculating loop and are later slide from the bottom to the top forming a straight line. The bacteria appear to have effused as it spreads outwards. This shows that Escherichia coli are not motile as it only spread out from the straight line. The third method is stab culture. Escherichia coli and Bacillus subtilis are grown by stabbing vertically into nutrient gelatine in a test tube. Gelatine which contains Escherichia coli remains solid while the gelatine that contains Bacillus subtilis turns into liquid. This shows that Bacillus subtilis produces an enzyme called gelatinase which will turn the solid gelatine into liquid form while Escherichia coli do not produce gelatinase. The last method is plate culture whereby Escherichia coli are grown by streaking on agar plates in Petri dishes. Quadrant streaking method and S-shaped streaking method are used in this experiment. In quadrant streaking method, Escherichia coli are found to be in the form of

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