Acid-fast stain

What is the molecule targeted and in what structure is it found?

Mycolic acid in the bacterial cell wall

What is the primary stain, counterstain, and decolorizer?

Primary stain: Carbolfuchsin

Counter stain: methylene blue

Decolorizer: Acid alcohol

What is the charge of the dyes used in this lab?

Both primary and counter stain are positive

What will happen if you forget to apply carbolfuchsin?

All cells stain with the counter stain, so acid-fast stain will be blue (acid-fast negative)

What will happen if you forget to decolorize with acid ethanol?

Acid-negative species keep the primary stain and will be pink (acid-fast positive)

What will happen if you over decolorize with acid ethanol?

WhPink color is washed from all cells and acid-fast positive will be blue (acid-fast negative)

What will happen if you forget to apply methylene blue?

Acid-fast negative do not get stained and will be clear

What color does an acid-fast positive bacterium appear? Acid-fast negative? Be able to differentiate between these two in pictures.

- Acid-fast positive bacterium: bright pink color (means there is mycolic acid in the cell wall)

- Acid-fast negative: Blue color (means they do not have mycolic acid in the cell wall)

Bacteria species:

Acid-fast + / - :

Mycobacterium smegmatis

Acid-fast positive

Bacteria species:

Acid-fast + / -:

Klebsiella pneumoniae

Acid-fast negative

Bacteria species:

Acid-fast + / - :

Streptococcus agalactiae

acid-fast negative

Bacteria species:

Acid-fast + / - :

Staphylococcus aureus

Acid-fast negative

Bacteria species:

Acid-fast + / - :

Escherichia coli

Acid-fast negative