Sterilization and Disinfection Concepts

Study Notes

Sterilization and Disinfection

Sterilization is the process of destroying or eliminating all microbial life, including spores
Disinfection reduces the number of microbes on a nonliving surface or object, making it safe for use
Antiseptics are chemicals used to reduce microbes on living tissue
Cleaning removes visible dirt from objects and surfaces using water and detergents. Cleaning is crucial before disinfection and sterilization

Organisms According to Resistance to Sterilization

Prions are the most resistant, followed by bacterial spores, mycobacteria, nonenveloped viruses, enveloped viruses, and fungi, and finally bacteria

Methods of Sterilization

Physical Methods:
- Radiation:
  - Gamma rays: used for transplant devices, packaged medical devices (e.g., syringes, gloves, catheters). The mechanism involves DNA breakage through ionization. This is a cold sterilization method
- Heat:
  - Dry Heat:
    - Red heat: used for metals (e.g., forceps)
    - Flaming: used for mouth of tubes, glass slides
    - Hot air oven: used for glassware, metals, and dry materials (oil, powders). Specific temperatures and times (150°C for 150 minutes, 160°C for 120 minutes, 170°C for 60 minutes) are used for effective sterilization. Sterilization control is done by using Bacillus atrophaeus spores.
  - Moist Heat:
    - Autoclave: uses saturated steam under pressure, raising the boiling temperature above 100°C to sterilize heat and moisture resistant items (surgical instruments, gowns, linens)
      - Sterilization cycles are standard (15 minutes at 121°C with 15 lbs. pressure); flash sterilization (134°C for 3-10 minutes) is used in emergencies; Prions require 134°C for 60 minutes
- Filtration: used to remove microorganisms from fluids and air by passing them through filters with small pores (bacterial filters have 0.22-0.45 µm pore size, viral filters have smaller pores).
  - Used for heat-labile substances (antibiotics, vaccines) and air sterilization (surgical masks, respirators, HEPA filters in surgical rooms, ICUs, isolation rooms, and microbiology safety cabinets).
Chemical Methods:
- Sterilant Gases: Ethylene oxide is used for heat- and moisture-sensitive devices (sutures, catheters, endoscopes) but needs aeration time (8-12 hours) afterward to remove residual gas, which is a disadvantage Sterilant gases are useful when the items being sterilized cannot tolerate heat.

Methods of Disinfection

Physical Methods:
- Radiation:
  - Ultraviolet (UV) Rays: Used to disinfect surfaces like operating theatres, biological safety cabinets, and isolation rooms; but penetration is limited
- Heat:
  - Moist Heat:
    - Boiling: used to disinfect items at 100°C for 15 minutes
    - Pasteurization: used to reduce microbes in foods and beverages, e.g., milk (63°C for 30 minutes, batch method; 72°C for 15 seconds, flash method). Rapid cooling is essential
Chemical Methods:
- Liquids:
  - High-level disinfectants: can kill bacterial spores (e.g., aldehydes, H2O2).
  - Intermediate-level disinfectants: kill all organisms except spores (alcohols, halogens).
  - Low-level disinfectants: kill a limited type of organisms, e.g., phenolics. These antiseptics are used for surgical skin preparation or environmental surfaces

Factors Affecting Sterilization and Disinfection

Agent concentration and stability
Number and type of microorganisms
Temperature and pH
Presence of organic matter
Physical nature of the object (hinges, lumens)
Presence of biofilms (a layer of microbes on surfaces)

Monitoring Efficiency

Physical monitoring: checking cycle time, temperature, and pressure
Biological monitoring: using spores of Geobacillus stearothermophilus (testing the autoclave)