LECTURE - Uncommon Stains: Microorganisms

Question 1

Ziehl Neelson stain

Answer 1

mycobacteria

Question 2

Warthin Starry

Answer 2

spirochetes

Question 3

Grocott’s methhenaine silver/PAS

Answer 3

fungi/pneumocystis

Question 4

modified gram stain is rarely done, why?

Answer 4

diagnostic yield is much lower in histology = organisms are dead so there is no opportunity to grow; stays at a low amount

Question 5

magnesium ribonucleate is present in

Answer 5

gram pos

Question 6

modified gram stain

Answer 6

• rarely done
• magnesium ribonuclease is present in gram pos
• cationic CV and iodine form a lake to bind Mg that resists differentiation = similar to micro
• contrasting colour added to stain gram neg
• contrasting colour to stain background (green)

Question 7

Ziehl Neelson

Answer 7

• cell wall of mycobacteria = high mycolic acid content
• cationic dye = carbol fuchsin entry accomplished by heat and soap or phenol
• differentiation step = wash away excess colour but due to high mycolic acid = retain colour after being forced in
• counterstain = methylene blue
• positive = ‘acid fast’

Question 8

Warthin Starry

Answer 8

• demonstrates spirochete = H. pylori, cat scratch fever, B. piliformis
• silver technique with 2 main steps
  > acidic silver nitrate = lower pH creates active groups on spirochetes
  > developing = addition of more silver to make spirochetes visible = precipitate active groups

Question 9

PAS/GMS

Answer 9

• Pneumocystis carinii/P.hirovecii cause penumonia opportunistically = cannot be cultured so relies on histo for diagnosis
• major cause of death in AIDS
• misclassified as a protozoan, now yeast-like fungus
• cannot culture
• PAS/GMS positive ; “little tea cups”