Ex 6:Smear Preparation- Simple Staining Flashcards
What are simple stains?
staining procedure that uses one stain
What is a simple direct stain?
stain that colours bacterial cells
What is simple negative stain?
stain that colours the background, leaves bacteria unstained
Why may cells be beaded?
when bacteria don not stain evenly, dark spots appear after dye is applied. rods mistaken for chain of cocci
What is bipolar staining?
the spots of stain are on the end of a cell. incorrect id of rods and cocci as diplococci
What do dyes/stains consist of?
they are salts with a cation and anion.
What is chromophore?
ion can be part of molecule that is brightly colored, the chromophore
What is the staining principle based on?
similar charges repel and vice versa. bacterial cell carry -ve charges in near neutral pH . attract molecules carrying +ive charges
What are basic dyes?
have +ively charged chromophores, that attract and colour cells
Name some basic dyes
methylene blue, crystal violet and safranin, malachite green
What are acid dyes?
have -ively charged chromophores are repelled by bacterial cells causing dye to colour background, cells are colourless
Name some acid dyes
nigrosin, Congo red and India ink
Which staining technique are basic and acid dyes used for?
basic- direct. acid- negative
Why are cells heat fixed?
to attach cells firmly to the slide
Why is excessive heating not ideal?
cells shrink more and heating warps the cells
