Quiz 5: Gram staining

1. Primary

2. Mordant

3. Decolorizing agent

4. Counter stain

Differential staining reagents

turns all cells its color

Primary stain

intensify the primary stain’s color

Mordant

establishes color contrast by removing the primary stain from the entire cell or only certain cell structures

Decolorizing agent

• has a color contrasting the primary stain

• if the primary color isn’t decolorized/washed out, this cannot absorb = cells retain primary color

• if washed out, cells will appear as this color

Counterstain

• named after Dr. Hans Christian Gram

• divides bacterial cells into g-neg & g-pos+

• stain rx is based on chem. components of bacterial cell walls

Gram stain

thick peptidoglycan layer

G-pos+ cell wall

• thin peptidoglycan layer

• surrounded by lipid-containing layers

G-neg cell wall

violet

color of primary stain

Iodine; binds the primary stain = appears purple-black

color of mordant

95% Ethyl alcohol

color of decolorizing agent