AP-Micro Microbiology: Specimen Processing and Stains 2

Question 1

Which fixative is commonly used to preserve bacterial morphology before Gram staining?

Accepted Answer

Heat fixation

Answer

Formalin

Answer

Glutaraldehyde

Answer

Ethanol immersion

Question 2

A sputum sample is collected from a patient suspected of having tuberculosis. What is the preferred transport medium?

Accepted Answer

No medium — direct smear within 1 hour

Answer

Thioglycolate broth

Answer

Stuart's transport medium

Answer

Löwenstein-Jensen slant at 4°C

Question 3

The Ziehl-Neelsen stain uses carbol fuchsin as the primary stain. What is its function?

Accepted Answer

It penetrates the waxy mycolic acid cell wall when heated

Answer

It stains the peptidoglycan layer red

Answer

It acts as a mordant to fix crystal violet

Answer

It decolorizes gram-negative organisms

Question 4

Which decolorizer is used in the acid-fast stain procedure?

Accepted Answer

Acid-alcohol (3% HCl in 95% ethanol)

Answer

Acetone-alcohol (95%)

Answer

Lugol's iodine

Answer

Safranin

Question 5

A CSF specimen arrives in the laboratory with a 4-hour delay at room temperature. Which organism is most at risk of being missed due to this delay?

Accepted Answer

Neisseria meningitidis

Answer

Cryptococcus neoformans

Answer

Streptococcus pneumoniae

Answer

Escherichia coli

Question 6

What does the counterstain safranin reveal in the Gram stain procedure?

Accepted Answer

Gram-negative organisms staining pink/red

Answer

Gram-positive organisms staining pink

Answer

Fungal elements staining red

Answer

Capsules staining pink

Question 7

India ink preparation of CSF is used to visualize which structure?

Accepted Answer

Fungal capsules

Answer

Bacterial flagella

Answer

Spore coats

Answer

Viral inclusion bodies