RMA Microbiology and Specimen Collection 3 — Questions and Answers
Question 1: Which staining method is used to differentiate bacteria into gram-positive and gram-negative groups?
- Gram stain (Correct answer)
- Acid-fast stain
- Wright stain
- India ink stain
Correct answer: Gram stain
The Gram stain separates bacteria by cell wall characteristics into gram-positive (purple) and gram-negative (pink/red).
Question 2: What color do gram-positive bacteria appear after Gram staining?
- Purple/blue (Correct answer)
- Pink/red
- Green
- Colorless
Correct answer: Purple/blue
Gram-positive bacteria retain the crystal violet stain and appear purple/blue.
Question 3: A specimen for anaerobic culture should be handled how?
- Transported quickly with minimal air exposure (Correct answer)
- Refrigerated for 24 hours before transport
- Exposed to air to kill contaminants
- Frozen immediately
Correct answer: Transported quickly with minimal air exposure
Anaerobic organisms die when exposed to oxygen, so specimens must be transported quickly with minimal air exposure.
Question 4: Which stain is specifically used to identify Mycobacterium tuberculosis?
- Acid-fast (Ziehl-Neelsen) stain (Correct answer)
- Gram stain
- Giemsa stain
- Methylene blue
Correct answer: Acid-fast (Ziehl-Neelsen) stain
The acid-fast stain detects mycobacteria, which resist decolorization due to their waxy cell wall.
Question 5: What is the minimum recommended volume for an adult blood culture per bottle to maximize pathogen detection?
- 8-10 mL (Correct answer)
- 1-2 mL
- 0.5 mL
- 20-25 mL
Correct answer: 8-10 mL
Filling each bottle with 8-10 mL of blood optimizes the sensitivity of blood culture detection in adults.
Question 6: Which type of media supports growth of most bacteria without selecting for specific organisms?
- Enriched/nonselective media like blood agar (Correct answer)
- Selective media like MacConkey agar
- Differential media only
- Anaerobic transport media
Correct answer: Enriched/nonselective media like blood agar
Blood agar is an enriched, nonselective medium that supports the growth of a wide range of bacteria.
Question 7: When a wound culture is ordered, the medical assistant should collect the sample from where?
- Deep within the wound after cleaning the surface (Correct answer)
- The dry skin around the wound
- The bandage covering the wound
- The surface crust only
Correct answer: Deep within the wound after cleaning the surface
Sampling from deep in the wound after surface cleaning yields the true infecting organisms rather than surface contaminants.
RMA Microbiology and Specimen Collection 3
Which staining method is used to differentiate bacteria into gram-positive and gram-negative groups?