Microbiology 1- Techniques
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How is excess fluid removed during a wet mount?
How is oil removed from the slide during a wet mount?
What are the steps of a methylene blue simple stain?
- 1. Stain smear for 60 seconds using methylene blue
- 2. Rinse off with tap water
- 3. Blot the smear gently with bibulous paper
- 4. Examine with microscope
Why is gram-stain used?
- Divides bacteria in 2 groups based on the structure of their cell wall
- Gram-positive or gram-negative
How does a gram-stain work?
If cell is gram-negative, the peptidoglycan is covered by the outer membrane, so it cannot absorb the stain
What are the steps of a gram-stain and the results of each step?
- Flood the heat-fixed smear with crystal violet for 1 min- all cells turn purple
- Add iodine solution for 1 min- all cells remain purple
- Decolorize with alcohol for 20 sec - gram-positive cells are purple; gram-negative cells are colourless
- Counterstain with safranin for 1-2 mins- gram positive cells are purple, gram-negative cells are pink-red
What are bacterial endospores?
- Produced by some gram-positive bacteria as a survival strategy
- Highly resistant to adverse conditions such as extreme temperature, drying, radiations, nutrient depletion, chemicals
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