STM 312 – MICROBIOLOGICAL TECHNIQUES 1 OSUNTECHCOLLEGE 2022/2023 First Semester Examination

ANWSER

Question 1:

Answer: Aseptic techniques refer to practices and procedures that prevent contamination of cultures, sterile media, and equipment by microorganisms. These techniques include sterilization, disinfection, and proper handling of materials in a microbiology lab.

Question 2:

Answer: Five common chemicals used for chemical sterilization include:

1. Ethanol (70%)
2. Hydrogen peroxide
3. Glutaraldehyde
4. Formaldehyde
5. Sodium hypochlorite (bleach)

Question 3:

Answer: Two examples of materials that can be sterilized using dry heat are:

1. Glassware (e.g., test tubes, Petri dishes)
2. Metal instruments (e.g., forceps, scalpels)

Question 4:

Answer: Procedures involved in operating an autoclave:

1. Load the materials into the autoclave, ensuring proper spacing for steam penetration.
2. Add water to generate steam.
3. Set the autoclave to 121°C at 15 psi for 15–20 minutes.
4. Allow the pressure to release before opening the autoclave.
5. Carefully remove sterilized materials using aseptic techniques.

Question 5:

Answer: Differences between pure culture and mixed culture:

• Pure Culture: Contains only one type of microorganism.
• Mixed Culture: Contains two or more different microorganisms.

Question 6:

Answer: Preparation of 100 mL of nutrient agar:

1. Weigh 2.8 g of nutrient agar powder.
2. Dissolve in 100 mL of distilled water.
3. Heat to dissolve completely.
4. Autoclave at 121°C for 15 minutes.
5. Cool slightly and pour into sterile Petri dishes.

Question 7:

Answer: Sterilization methods and chart representation:

Experiment Two

Question 8:

Answer: To make a bacterial smear on a microscope slide:

1. Place a drop of distilled water on a clean slide.
2. Use a sterile loop to collect bacteria and mix with water.
3. Spread into a thin layer.
4. Air dry and heat-fix by passing over a flame.

Question 9:

Answer: Gram staining procedure:

1. Apply crystal violet (primary stain) for 1 minute, then rinse.
2. Apply iodine (mordant) for 1 minute, then rinse.
3. Decolorize with ethanol or acetone for 10–15 seconds, then rinse.
4. Apply safranin (counterstain) for 1 minute, then rinse and dry.

Question 10:

Answer: The stain that gives a smear a blue/purple color is Gram stain (crystal violet).

Question 11:

Answer: Another name for Gram’s/Lugol’s iodine is Mordant.

Question 12:

Answer: Generally, 2–3 drops of stain are required for Gram staining.

Question 13:

Answer: Buffer definition: A buffer is a solution that resists changes in pH when an acid or base is added.

• Types:
  1. Acidic buffer (e.g., Acetic acid + Sodium acetate)
  2. Basic buffer (e.g., Ammonia + Ammonium chloride)
• Mechanism: Buffers maintain pH by absorbing excess H+ or OH⁻ ions.

Question 14:

Answer: Ten microbiology lab practices and safety rules:

1. Wash hands before and after lab work.
2. Disinfect work surfaces before and after use.
3. Wear appropriate personal protective equipment (PPE).
4. Work near a Bunsen burner for aseptic techniques.
5. Avoid eating or drinking in the lab.
6. Properly label all cultures and chemicals.
7. Dispose of biological waste properly.
8. Always sterilize inoculating loops before and after use.
9. Do not pipette by mouth.
10. Report spills and accidents immediately.