Microbiology: Specimen Processing and Stains Flashcards

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

Answer: Gomori methenamine silver (GMS) stain

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

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

Answer: It contains charcoal to absorb toxic fatty acids

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

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

Answer: Auramine-rhodamine fluorochrome stain

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

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

Answer: Formalin plus PVA (two-vial system)

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

Calcofluor white stain is particularly useful for detecting which organisms?

Answer: Fungi and Acanthamoeba cysts

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

What is the recommended minimum volume of blood for each blood culture bottle in adults?

Answer: 10–20 mL

Inoculating 10–20 mL per bottle significantly increases the sensitivity of blood cultures for detecting bacteremia.

Spores of Clostridium species appear as which color after a Schaeffer-Fulton endospore stain?

Answer: Red

In the Schaeffer-Fulton method, spores retain malachite green and then appear red after safranin counterstaining, while vegetative cells stain pink-red.