4.1.1.6
Microbiology
For hospitals, choosing the right antiseptics or antibiotics to achieve the appropriate hygiene levels is essential. The correct dilution is also important: a concentration high enough to work, but not so high as to be wasteful. You will investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zones of inhibition. The most effective antiseptic or antibiotic will prevent the growth of bacterial. Learning outcomes
Maths skills required
Formulae
Investigate the effects of antiseptics.
Measure diameters accurately.
Calculate cross-sectional areas of colonies or clear areas around colonies using
Calculate the area of your zone of inhibition.
area = πr ² where r = half of the mean diameter.
Suggest improvements to methods to reduce the growth of bacteria. Apparatus list one agar plate of bacterial cultures, readymade and NOT incubated (Bacillus subtilis, Escherichia coli, or Micrococcus luteus)
chromatography paper discs cut with a hole punch beaker of disinfectant five different antiseptic solutions
five pairs of sterile forceps
eye protection
adhesive tape Safety notes
After you have incubated your plates, make sure they have extra sticky tape around the edge. You do not want any of these bacteria escaping! If you are using ethanol to sterilise to equipment, make sure it is kept well away from any naked flames. Ethanol is very flammable and will catch fire. DISINFECTION: You are dealing with bacteria. Disinfection is VERY important! All equipment and materials and work surfaces must be disinfected using excess 1% Virkon for at least 10 minutes. Always wear eye protection when using Virkon solution. Wash your hands both before and after this practical. Common mistakes Be careful not to rush your work. While it is important to work quickly in order to minimise contamination, you need to be methodical and careful in your work. Make sure you don’t put tape all the way around your closed agar plate. Condensation in the plate needs to be able to escape and oxygen needs to get in. Clear zones might not be perfectly circular. To get an accurate diameter, measure the diameter twice (at 90° to each other) and calculate a mean diameter for each clear zone.
AQA GCSE (9–1) Biology Required Practicals Lab Book
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