AP-Micro Microbiology: Specimen Processing and Stains 3

Question 1

Which stain is the gold standard for identifying Pneumocystis jirovecii in bronchoalveolar lavage specimens?

Accepted Answer

Gomori methenamine silver (GMS) stain

Answer

GMS stain blackens the cell wall of fungal organisms including Pneumocystis jirovecii cysts against a green background.

Question 2

A wound swab is collected and transported in Amies transport medium. What is the primary advantage of this medium over Stuart's medium?

Accepted Answer

It contains charcoal to absorb toxic fatty acids

Answer

Amies medium contains charcoal that neutralizes toxic fatty acids on swabs, improving survival of fastidious organisms.

Question 3

Which staining technique uses fluorescent dyes and is useful for rapid screening of mycobacteria in sputum?

Accepted Answer

Auramine-rhodamine fluorochrome stain

Answer

Auramine-rhodamine binds mycolic acids and fluoresces under UV light, allowing faster low-power scanning for acid-fast bacilli.

Question 4

A stool specimen for ova and parasite (O&P) examination should ideally be preserved in which fixative?

Accepted Answer

Formalin plus PVA (two-vial system)

Answer

The two-vial system uses formalin for concentration techniques and PVA for permanent stained smears to maximize detection.

Question 5

Calcofluor white stain is particularly useful for detecting which organisms?

Accepted Answer

Fungi and Acanthamoeba cysts

Answer

Calcofluor white binds to chitin in fungal cell walls and cellulose in Acanthamoeba cysts, fluorescing bright white-blue under UV.

AP Practice Test