2.1.1 Flashcards
What are the four ways samples can be prepared?
Dry mount, wet mount, squash slides, smear slides
How is a dry mount prepared?
Solid specimens are viewed whole or are cut into thin slices, called sectioning. The specimen is then placed on the centre of the slide and a cover slip is placed on the sample
How is a wet mount prepared?
Specimens are suspended in a liquid. A cover slip is placed on from an angle
How is a squash slide prepared?
A wet mount is prepared, and then a lens tissue is used to press down on the cover slip.
How is a smear slide prepared?
The edge of a slide is used to smear the sample, creating a thin even coating on another slide. A cover slip is then placed on top of the sample
Why is staining used?
To increase contrast
Give two examples of positively charged dyes
Crystal violet and methylene blue
Give two examples of negatively charged dyes
Nigrosin and congo red
What are the positively charged dyes attracted to?
Negatively charged materials in the cytoplasm, so cell components are stained
How do the negatively charged dyes work?
They are repelled by the negatively charged cytosol, so the dyes stay outside the cells, leaving them unstained, and so they stand out against the stained background
How is differential staining helpful?
It can help distinguish between two types of organisms that would be otherwise difficult to identify
Why is gram staining used?
Gram staining technique is used to separate bacteria into Gram-positive and Gram-negative bacteria.
How is gram staining used?
Crystal violet is first applied to a bacterial specimen on a slide, ad then iodine, fixing the dye. The slide is washed with alcohol. The gram-positive retain the stain and appear blue, but the gram-negative bacteria lose the stain. They are then stained with safraning dye, which is a counterstain, causing them to appear red.
Why is acid-fast technique used?
It is used to different species of Mycobacterium from other bacteria
How is acid-fast used?
A lipid solvent is used to carry carbolfuchsin dye into the cells. The cells are washed with a dilute acid-alcohol solution. Mycobacterium are not affected by the acid-alcohol and so retain the stain, but others lose it and they are exposed to methylene blue
