Differential Stains

When gram staining what happens to bacteria with a thick cell wall and give an example of a bacterium? What is this called? (3)

• They will retain the primary stain crystal violet and appear purple

• Gram positive

• eg. Streptococcus pyogenes

What happens when a bacteria with a thin cell wall is gram stained and give an example? What is this called? (3)

• The bacteria loses the primary stain crystal violet during destaining, and later on takes on the counterstain’s (safranin) color of pink

• This is Gram negative

• eg. E coli

How does the gram staining work? (4)

1) Regular single stain routine

2) Add Crystal Violet (primary stain) then wash (cell stains purple)

3) Add Iodine (mordant) then wash (Helps primary stain stick to gram positive cells)

4) Add Alcohol (decolorizer/destainer) then wash (removed purple stain from gram negative cells)

5) Add Safranin (counterstain) then wash, pat dry and view (adds pink stain to gram negative cells)

What does a spore stains do and give an example of a bacterium this would be used on? (4)

• Stains an internal structure (spores/endospores) of some bacteria

• Primary stain is green

• Counterstain (safranin) stains rest of the cell red

• eg. Bacillus Anthracis

What does a Flagella stain do? And what does the mordant do? (2)

• Stains an external structure (flagella)

• Mordant thickens Flagella so they can be observed with a light microscope

What does the acid fast stain do? (3)

• Uses Carbol Fuschin to detect presence of waxy compound (myolic acid) in the cell wall

• Counterstain methylene blue is used to stain non acid-fast bacteria and tissues blue

What genus of bacterium can the acid fast stain be used to identify and some examples: (3)

• Mycobacterium

• tuberculosis

• leprae

What is the Capsule stain used for and give an example of a bacteria it is used for: (5)

• Used to detect thick layer polysaccharide outside of cell (known as capsule)

• Negative stain colors backround

• Positive stain colors cell

• Capsule rarely takes dyes (stays colorless)

• Eg. streptococcus pneumoniae