MicroBio Lab Practical

How long is crystal violet left on for a simple stain?

• 5 to 10 minutes
• 30 seconds to 1 minute
• 10 to 15 minutes
• 1 to 5 minutes

How long is Methylene blue left on for a simple stain?

• 5 to 10 minutes
• 30 seconds to 1 minute
• 10 to 15 minutes
• 1 to 5 minutes

How long is safranin left on for a simple stain?

• 5 to 10 minutes
• 10 to 15 minutes
• 1 to 5 minutes
• Up to 1 minute

Put in order the steps of a blood smear stain and observation:

1. Stain (Blue) — dip 5× for 1 s each, drain excess.

• 2. Increase to 40×; focus on middle region with normal RBCs.

• 3. Fix in Stain (Green) — dip 5× for 1 s each, drain excess.

• 4. Once smear is dry, bring slide to Coplin jars.

• 5. Scan for WBCs under low power; view in higher powers.

• 6. On low power (10×), examine area just in from feathered edge where RBCs touch.

• 7. Rinse in distilled water (replace often); air-dry.

• 8. Stain (Red) — dip 5× for 1 s each, drain excess.

Put the order in which a simple stain is done:

1. 1. Hold slide at angle; gently rinse with distilled water into tray.

2. 2. Heat-fix slide by passing over flame until water evaporates (do not overheat).

3. 3. Blot dry with bibulous paper (do not rub).

4. 4. Place slide in staining tray; apply stain

5. 5. Observe under oil immersion.

6. 6. Wear gloves and goggles; prepare bacterial emulsion/smear and allow ~2 min to air-dry.

What are the correct steps in Negative stain:

1. 1. Air-dry slide; do not heat-fix.

2. 2. Using second clean slide at ~30° angle, draw back into drop; once it flows across width, push spreader to far end.

3. 3. Place drop of nigrosin near one end of clean slide; aseptically add organism and emulsify with loop.

4. 4. Observe under microscope.

5. 5. Wear gloves and goggles; place clean paper towel on bench. Do not heat-fix for this smear.

Correct steps for a gram stain:

1. 1. Blot dry with bibulous paper; observe under oil immersion.

2. 2. Apply safranin for 1 min.

3. 3. Immediately rinse with distilled water.

4. 4. Wear gloves/goggles; prepare bacterial emulsion/smear for three organisms; air-dry; heat-fix slides.

5. 5. Apply crystal violet for 1 min.

6. 6. Practice with additional slides to master technique.

7. 7. Rinse gently with distilled water.

8. 8. Decolorize with acid/alcohol until runoff is clear (15–30 drops).

9. 9. Apply iodine (mordant) for 1 min.

For how long is the crystal violet left on to stain in Gram staining?

• 30 seconds
• 1 minute
• 2 minutes
• 5 seconds

How long is Iodine left on during Gram staining?

• 5 seconds
• 2 minutes
• 30 seconds
• 1 minute

How long do you leave decolorizer/acid/alcohol on Gram staining?

• 5-15 seconds
• 30-50 drops

• 10-30 seconds
• You put as many drops until it runs clear.