C1.4 Microbiology
- Created by: annabelk
- Created on: 04-02-23 18:20
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- MICROBIOLOGY
- Classification of bacteria
- Colour
- Colonising characteristics
- Single
- Pair
- Cluster
- Chain
- Gram staining
- The process:
- 1. Pass microscope slide containing bacteria over bunsen burner to fix bacteria
- 2. Apply crystal violet dye
- 3. Bind crystal violet to bacteria with iodine
- 5. Stain gram- bacteria pink using saffranin
- 4. Wash off excess crystal violet with ethanol
- Gram +
- Stain purple
- Thick peptidoglycan cell wall to retain more crystal violet
- No lipopolysaccharide layer
- Gram -
- Stain pink
- Lipopolysaccharide layer prevents entry of crystral violet to peptidoglycan cell wall
- This gives gram- antibiotic and lysozyme resistance
- Ethanol destroys lipopolysaccharide layer, so can be stained by saffranin
- Thinner peptidoglycan cell wall retains less dye
- The process:
- Shape
- Bacillus (rod shape)
- Coccus (spherical)
- Spirillum (spiral)
- Size
- Conditions for bacterial growth
- Growth factors
- e.g. vitamins, minerals
- Correct oxygen
- Obligate aerobes- need oxygen for growth
- Obligate anaerobes- can't grow in the presence of oxygen
- Facultative anaerobes- ca grow with or without oxygen (prefer with oxygen)
- Temperature
- Must be optimum for enzyme function
- For human pathogens, this is 37C
- Source of nitrogen and carbon
- Nitrogen = amino acid synthesis
- Carbon = biological molecule synthesis
- pH
- Must be optimum for enzyme function
- Mose bacteria prefer slightly alkaline
- Growth factors
- Measuring bacterial growth
- Total count- the number of bacteria, dead and alive, in a sample
- Viable count- the number of alive bacteria in a sample
- Serial dilutions
- Underestimate (assumes 1 bacteria gave rise to a colony)
- Serial dilutions
- Haemocytometer
- Turbidimetry
- Aseptic technique
- Prevents contamination of environment with experimental bacteria or experimental bacteria with environmental bacteria
- Examples
- Work near bunsen burner (convection currents)
- Wash hands
- Wipe down work surface
- Keep lid on
- Use sterilised equipment
- Reduce drafts
- Methods of sterilisation
- Irradiation
- Heat
- Autoclave at 121C for 15min
- Classification of bacteria
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