Physical method of sterilization

• Sterilization is a crucial process in microbiology, medicine, and various industries to ensure the elimination of all forms of microbial life, including spores.
• Physical methods of sterilization, particularly dry heat and moist heat, are widely used.

Dry Heat Sterilization

• Principle:

  • Dry heat sterilization utilizes hot air devoid of moisture, making it less efficient at heat transfer compared to moist heat methods.
  • Microorganisms are eradicated through oxidative damage and protein denaturation when exposed to high temperatures for extended periods.

• Equipment

  • Hot Air Oven:

    • An insulated chamber fitted with heating elements and a fan to ensure even circulation of hot air.
    • Uses hot air circulated at 160-170°C for 2 hours.
  • Here is a table showing the temperature and time required for sterilization using a hot air oven:

Temperature (°C)	Time
160°C	2 hours
170°C	1 hour
180°C	30 minutes

• This table provides the standard conditions for dry heat sterilization in a hot air oven.

• Detailed Procedure

• Preparation:

  • Cleaning and Drying: Ensure items are clean and completely dry.
  • Packaging: Place items in heat-resistant containers or wrap in aluminum foil.

• Loading the Oven:

  • Arrange items for adequate air circulation, avoiding overcrowding.

• Setting Parameters:

  • Standard conditions:
  • 160°C for 2 hours
  • 170°C for 1 hour
  • 180°C for 30 minutes

• Operation:

  • Heating: Preheat the oven to the set temperature before loading.
  • Exposure: Begin timing once the oven reaches the target temperature.
  • Monitoring: Use sensors to ensure uniform heat distribution.

• Cooling:

• Merits

  • Effective for Anhydrous Materials: Ideal for sterilizing glassware, metal instruments, and powders that can be damaged by moisture.
  • No Corrosion: Does not cause rusting or corrosion of metal instruments.
  • Penetrates Thick Materials: Suitable for materials that can tolerate high temperatures.

• Demerits

  • Longer Time: Requires longer exposure times compared to moist heat.
  • High Temperatures: Not suitable for heat-sensitive materials (e.g., plastics, rubber).
  • Energy Intensive: Requires more energy to maintain high temperatures.

• Applications

  • Glassware and Metal Instruments: Sterilization of glass Petri dishes, flasks, and surgical instruments.
  • Powders and Oils: Sterilization of non-aqueous substances that cannot be exposed to moisture.
  • Waste Disposal: Incineration of biological waste and contaminated materials.

Moist Heat Sterilization

Principle

• Moist heat sterilization uses steam under pressure to kill microorganisms through protein denaturation and coagulation.
• This method is more efficient than dry heat because steam penetrates materials more effectively, transferring heat more rapidly.

Equipment:

Autoclave:

• A sealed chamber that uses steam under pressure to sterilize various materials.

Here is a table showing the temperature, steam pressure, and holding time required for sterilization using an autoclave:

Temperature (°C)	Steam Pressure (psi)	Holding Time
121°C	15 psi	15-20 minutes
126°C	20 psi	10 minutes
134°C	30 psi	3-5 minutes

This table outlines the standard conditions used for moist heat sterilization in an autoclave.

Procedure:

1. Preparation:

   • Place items in autoclave-safe containers or wrap in autoclave paper.
   • Avoid overloading for proper steam circulation; use autoclave tape as an indicator.

2. Setting Parameters:

   • Temperature: 121°C (up to 134°C per protocol).
   • Pressure: 15 psi (103.4 kPa).
   • Time: 15-20 minutes, adjusted for load size.

3. Operation:

   • Secure the door and select the cycle.
   • Vent air to avoid pockets. Monitor conditions with gauges and indicators.

4. Cooling and Drying:

   • Depressurize gradually; some autoclaves have a drying cycle.

5. Unloading:

   • Wear gloves, vent steam carefully, and let items cool before handling.

Merits

1. Effective Sterilization: More effective at lower temperatures and shorter times compared to dry heat.
2. Broad Applicability: Suitable for a wide range of materials, including heat-sensitive items like culture media and biological fluids.
3. Penetration: Steam penetrates porous materials, ensuring thorough sterilization.

Demerits

1. Moisture Damage: Not suitable for materials that can be damaged by moisture (e.g., electronics).
2. Corrosion: Can cause corrosion of metal instruments over time.
3. Pressure Hazards: Requires careful handling of high-pressure equipment to avoid accidents.

Applications

1. Medical and Laboratory Equipment: Sterilization of surgical instruments, culture media, and glassware.
2. Microbiological Media: Sterilization of agar and broth media used for bacterial culture.
3. Pharmaceuticals and Food: Sterilization of injectable solutions, canned foods, and beverages through pasteurization.

Thank you for reading from Firsthope's notes, don't forget to check YouTube videos!