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Microbiology: Specimen Processing and Stains Flashcards

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  1. What is the purpose of iodine (Gram's iodine) in the Gram stain procedure?

    Answer: Mordant that fixes crystal violet in gram-positive cells

    Gram's iodine acts as a mordant, forming a crystal violet-iodine complex that is trapped within the thick peptidoglycan of gram-positive organisms.

  2. Which of the following organisms would appear as 'weakly acid-fast' using a modified Kinyoun stain with 1% sulfuric acid?

    Answer: Nocardia species

    Nocardia species are weakly acid-fast, retaining modified decolorizer (1% H2SO4) but not the strong acid-alcohol used for Mycobacterium.

  3. A urine culture is plated within 2 hours of collection. If processing is delayed, urine should be stored at:

    Answer: 4°C to slow bacterial growth

    Refrigeration at 4°C slows bacterial multiplication, preventing falsely elevated colony counts if the specimen cannot be processed immediately.

  4. The Kinyoun acid-fast stain differs from the Ziehl-Neelsen method in that it:

    Answer: Does not require heat for dye penetration

    Kinyoun's method is a 'cold' acid-fast stain using a higher concentration of carbol fuchsin, eliminating the need for heating the slide.

  5. Giemsa stain is particularly useful in microbiology for identifying which of the following?

    Answer: Intracellular organisms such as Chlamydia inclusions and malaria parasites

    Giemsa stains nuclei blue-purple and cytoplasm pink, making it excellent for visualizing intracellular organisms and blood-borne parasites.

  6. For optimal recovery of anaerobes from a wound, the specimen should be transported in:

    Answer: Pre-reduced anaerobically sterilized (PRAS) transport vial

    PRAS vials have been pre-reduced to remove oxygen and contain reducing agents, maintaining anaerobic conditions essential for obligate anaerobe survival.

  7. A laboratory technician observes gram-positive cocci in clusters on a Gram stain of a wound aspirate. This morphology is most consistent with which genus?

    Answer: Staphylococcus

    Staphylococcus species characteristically divide in multiple planes, forming grape-like clusters visible on Gram stain.