Microbiology Lab Test Review: Essential Practicum Guide for Students
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30 cards
Question: Name this Technique: Gram stain — Which cell types stain positive (Gram-positive) and which negative (Gram-negative)?
Answer: Gram-positive cells are positive (retain crystal violet and appear purple); Gram-negative cells are negative (do not retain crystal violet after decol
Question: Gram stain — What are you staining for?
Answer: Staining for differences in bacterial cell wall structure (thick peptidoglycan in Gram-positive vs. thin peptidoglycan plus outer membrane in Gram-neg
Question: Gram stain — Name the steps.
Answer: 1) Crystal violet (primary stain) 2) Iodine (mordant) 3) Alcohol/acetone (decolorizer) 4) Safranin (counterstain).
Question: Gram stain — How do you know positive vs negative?
Answer: Gram-positive: purple after procedure; Gram-negative: pink/red after counterstain.
Question: Name this Technique: Acid-fast stain — Which cell types are positive and which negative?
Answer: Acid-fast positive cells (e.g., Mycobacteria) retain the primary stain; acid-fast negative cells do not and take up the counterstain.
Question: Acid-fast stain — What are you staining for?
Answer: Staining for mycolic acid–rich cell walls (acid-fastness due to high lipid/mycolic content).
Question: Acid-fast stain — Name the steps.
Answer: 1) Apply carbol fuchsin (primary stain) with heat 2) Decolorize with acid-alcohol 3) Counterstain with methylene blue or similar. Positive cells remai
Question: Name this Technique: Endospore stain — Which cell types are positive and which negative?
Answer: Endospore-positive cells produce and contain endospores; endospore-negative cells do not and will not show spores.
Question: Endospore stain — What are you staining for?
Answer: Staining for bacterial endospores (highly resistant, dormant structures).
Question: Endospore stain — Name the steps.
Answer: 1) Apply malachite green with heat to stain spores 2) Rinse (spores retain stain) 3) Counterstain vegetative cells with safranin. Spores appear green;