Clinical use of light microscope

Since microorganisms are colorless what do we use to view them better? (1)

Stains

What are stains composed of and which stain do we use? (2)

• Composed of positively and negatively charged ions

• Use chromophore (colored ion)

What is a simple stain? (1)

Only one dye is used to highlight the microorganism

What are the 4 steps to apply a stain and view the microorganism? (4)

• Smear sample on slide and let it air dry

• (Fix with heat) Waft slide lightly over flame so the sample will stick on to the slide

• Add the stain

• Wash, pat dry, then view stained specimen

How do stains work? (3)

• Bacteria have net negative charge on their outer surface

• attracts stains with positively charged chromophore

• repels stains with negatively charged chromophore

What happens when you try using a positive stain on a bacterium and give an example of one. (3)

• The stain will bind to the bacterium

• Bacterium appears coloured, Back-round is clear

• eg. Crystal Violet

What happens when you try to use a negative stain on a bacterium? (3)

• Will not bind to bacterium

• Bacterium appears colourless, Backround is colored

• eg. nigrosin

What is a Differential stain? (1)

Stains that react differently based on the bacteria (helps to distinguish them)