Chapter 44 Staining Specimens

Gram stain

• used to categorize bacteria

• Requires 4 steps

  • Primary stain

  • mordant

  • decolorizer

  • counterstain

when doing stain, make sure to note shape of the bacteria and if gram negative or positive

Primary stain

• usually crystal violet

Mordant

• fixes dye to structures (cell wall)

• is usually idonine

Decolorizer

• 95% ethanol or acetone

counterstain

• basic fuchsin or safranin

Potassium Hydroxide test

• KOH

• determines true gram status

  • used when getting a gram variable reaction from the gram stain

Ziehl-Neelsen stain

• primaryily used to detect acid-fast organims

  • Mycobacterium and Nocardia species

• three steps

  • Primary stain (dimethyl sulfoxide (DMSO) and carbol fushin

  • Decolorizer - acid alcohol

  • counterstain - methylene blue

Giemsa stain

• used to detect spirochetes and rickettsiae and the capsule of Bacillus anthracis and the morphology of Dermatophilus congelnsis

• used to detect Borrelia burgdoferi spirochetes

Gram Negative color

• stains pink/red

Gram Positive color

• stain purple