Staining Flashcards
What is differential staining?
Makes it easier to tell between 2 types of organism
Give explanation of crystal violet + methylene blue:
Stain is positively charged + attracted to negatively charged cell components
Give explanation of iodine:
Stains plant cells since it stains starch blue/black
Explain negative staining:
- Background stained leaving specimen untouched
- E.g: Nigrosin + Congo red
- They’re negatively charged + repelled by cytosol (cytoplasm)
What are the 4 steps to pre-prepare slides?
Fixing, sectioning, staining, and mounting
Define fixing:
Chemicals used to preserve specimen in near-natural state
Explain sectioning:
- Specimens dehydrated with alcohols
- Put into mould with wax or resin to form block
- Sliced thinly with microtome (knife)
Explain staining:
Specimens treated with stains to show structures
Explain mounting:
Specimens secured to microscope slide, cover slip ontop
What is the gram stain technique used for?
Used to separate bacteria into 2 groups: Gram-positive and Gram-negative bacteria
What is the acid-fast technique used for?
Used to differentiate species of mycobacterium from other bacteria
How to do the gram stain technique:
- Crystal violet applied to specimen, then iodine, which fixes dye on slide
- Slide washed with alcohol
- Gram-positive bacteria keeps crystal violet stain (blue/purple)
- Gram-negative bacteria lose stain due to thinner cell walls
- Stain with safranin dye (counterstain), bacteria will look red
Is gram-positive bacteria susceptible to penicillin?
Yes, stops formation of cell walls
Is gram-negative bacteria susceptible to penicillin?
No, and has thinner cell walls
How to do the acid-fast technique:
- Lipid solvent carries carbolfuchsin dye into cells
- Cells washed with dilute acid-alcohol solution
- Mycobacterium isn’t affected by acid-alcohol - keeps red carbolfuchin stain
- Other bacteria loses stain + turns blue from exposure to methylene blue stain
