Updated: 5/9/2019

Stains

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Overview
  • Gram stain
    • Gram-positive bacteria have a thick peptidoglycan layer in their cell walls that holds the crystal violet stain
    • Gram-negative bacteria cannot hold the crystal violet stain and are counterstained by safranin
  • Giemsa stain
    • Borrelia
    • Plasmodium
    • trypanosomes
    • Chlamydia
  • Periodic acid-Schiff stain (PAS)
    • glycogen
    • mucopolysaccharides
    • used to diagnose Whipple's disease (Tropheryma whippelii)
  • Carbolfuscin
    • acid-fast stain
  • Ziehl-Neelsen
    • acid-fast organisms
      • Mycobacterium
      • Nocardia (partially acid fast)
      • Cryptosporidum oocysts
  • India ink
    • Cryptococcus neoformans 
      • stain is not taken up by polysaccharide capsule, creating a transparent halo
      • mucicarmine can also be used to stain capsule red
  • Silver stain
    • fungi
      • e.g. Pneumocystis, Legionella
Bugs that Gram stain poorly
  • Treponema
    • to thin to be visualized
    • use darkfield microscopy or fluorescent antibodies
  • Rickettsia
  • Mycobacteria
    • high-lipid-content cell wall
    • use acid-fast stain 
  • Legionella pneumophila
    • intracellular parasite
    • use silver stain
  • Mycoplasma
    • no cell wall 
  • Ureaplasma #9172
    • no cell wall
  • Chlamydia
    • intracellular parasite
    • has a cell wall but the cell wall does not contain peptidoglycan
 

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(M1.MC.15.75) A 71-year-old man who immigrated from Russia presents with a chronic cough. He reports that his cough has progressively worsened, and now his sputum contains small amounts of blood. A chest radiograph is obtained (Figure A), and a sputum sample is taken. Which of the following is an appropriate technique for microscopically identifying the underlying cause of this patient's condition? Tested Concept

QID: 106717
FIGURES:
1

Crystal-violet stain

4%

(2/45)

2

Safranin stain

11%

(5/45)

3

India ink

13%

(6/45)

4

Aniline dye then decolorizing with acid alcohol

27%

(12/45)

5

Periodic acid-Schiff stain

38%

(17/45)

L 1 D

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