Gamma Rays and Filtration Sterilization Quiz

Sterilization and Disinfection

• Sterilization is the process of destroying all microbial life, including spores.
• Disinfection reduces the number of microbes on a nonliving surface, making it safe for use.
• Antiseptics are chemicals that 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 Resistance to Sterilization

• Organisms resist sterilization to varying degrees.
• The order of resistance (from most to least resistant) is:
  • Prions
  • Bacterial spores
  • Mycobacteria
  • Nonenveloped viruses
  • Fungi
  • Bacteria
  • Enveloped viruses

Methods of Sterilization

• Physical methods include:
  • Radiation: Gamma rays are highly penetrating and effective at low temperatures. Used for transplant devices, medical devices, etc.
  • Heat:
    • Dry heat: Hot air ovens, flaming, incineration. Effective for glassware, metals, dry materials.
    • Moist heat: Autoclaves use pressurized steam to sterilize heat- and moisture-resistant items such as surgical instruments, gowns, linens, etc.
• Chemical methods include:
  • Sterilant Gases: Ethylene oxide is used for heat and moisture-sensitive devices (e.g., sutures, catheters, endoscopes), but it's flammable, toxic, and requires aeration time to eliminate residues.

Dry Heat Sterilization

• Red heat: Used for metals like forceps.
• Flaming: Used for sterilizing mouth/parts of tubes, glass slides
• Hot air oven: Used to sterilize glassware, metals, and dry materials. Optimal conditions: 150°C for 150 minutes, 160°C for 120 minutes, or 170°C for 60 minutes.

Autoclave (Moist Heat)

• Uses saturated steam under pressure to raise the boiling point above 100°C.
• Effective for heat- and moisture-resistant items.
• Three key parameters: temperature, time, and pressure.
• Standard cycle: 15 minutes at 121°C with 15 pounds pressure.
• Flash cycle: 134°C for 3-10 minutes for emergencies; Prions require 134°C for 60 minutes.

Hot Air Oven

• Electrically heated, controlled by thermostat.
• Optimal sterilization conditions: 150°C for 150 minutes, 160°C for 120 minutes, or 170°C for 60 minutes.
• Used for glassware (good quality), metals, and dry materials like oil and powders.
• Spores of Bacillus atrophaeus are used as a sterilization control.

Monitoring Autoclave Sterilization

• Physical monitoring: Checks cycle time, temperature, and pressure.
• Biological monitoring: Uses spores of Geobacillus stearothermophilus.

Ionizing Radiation (Gamma Rays)

• Mechanism: Ionization breaks DNA.
• Advantages: High penetrating power, cold sterilization.
• Uses: Transplant devices, packaged medical devices (syringes, surgical gloves, catheters).

Sterilization by Filtration

• Principle: Removes microorganisms by passing through filters with small pores.
• Uses: Sterilizing fluids containing heat-sensitive substances (antibiotics, vaccines), and sterilizing air.
• Membrane Filters: Used for fluids and air. Bacteria filters use 0.22–0.45µm pore size, while Viral filters use smaller pores. Filters are used in surgical masks and respirators, in HEPA filters (used in surgical rooms, ICUs, and safety cabinets), and in air sterilization.

Chemical Methods (Sterilization by Gases)

- **Ethylene Oxide:** Used for heat and moisture-sensitive devices, but requires aeration to remove residue (8-12 hours).  It's flammable and toxic.

Disinfection by Physical Methods

• UV radiation: Effective for denaturing DNA; but poor penetration and requires long exposure times. Used in operating theatres, biological safety cabinets, and isolation room surfaces.

Disinfection by Moist Heat

• Boiling: 100°C for 15 minutes.
• Pasteurization: Used for milk and other drinks using methods like:
  • Batch method: 63°C for 30 minutes, followed by rapid cooling.
  • Flash method: 72°C for 15 seconds, followed by rapid cooling. Examples include Mycobacterium bovis and Brucella spp.

Methods of Chemical Disinfection

• High-level disinfectants: Can kill bacterial spores (Aldehydes, H2O2).

• Intermediate-level disinfectants: Kill all organisms except spores (Alcohol, Halogens).

• Low-level disinfectants: Kill limited organisms (Phenols).

• Halogens (e.g., iodine, chlorine, sodium hypochlorite): Used as antiseptics for wound cleaning and surgical prep, and as disinfectants for water supplies, swimming pools, and surface spills.

• Alcohol: Used in various concentrations (70–80%) for handrubs, and cleaning of stethoscopes and ultrasound machines.

• Phenols: Used as antiseptics (e.g., Dettol) and disinfectants for environmental surfaces like bedside tables.

• Aldehydes (e.g., glutaraldehyde, formaldehyde): Glutaraldehyde are strong disinfectants, effective against bacterial spores, and used to sterilize endoscopes and microbiology lab surfaces. Formaldehyde is used for preservation of anatomical specimens, but it's limited due to fumes and potential carcinogenicity.

• Hydrogen Peroxide: Used for contact lenses and wound cleaning.

Factors Affecting Disinfection and Sterilization

• Agent concentration/stability
• Number and type of microorganisms
• Temperature and pH
• Organic or interfering substances
• Physical characteristics of the object
• Presence of biofilms

Test Your Knowledge Answers (Matching)

• Provided in the slides.