Sterilization and Disinfection

Sterilization and Disinfection - Defining the Battle

• Sterilization: Kills ALL microbes, including spores.

• Disinfection: Kills most pathogens (not spores) on objects.

  • Antisepsis: Disinfection of living tissue.

• Asepsis: Prevents microbial contamination.

• -cidal: Kills microbes.

• -static: Inhibits growth.

• Levels of Disinfection:

  • High (HLD): Kills all microbes, some spores (e.g., glutaraldehyde).
  • Intermediate (ILD): Kills M. tb, most viruses/fungi; no spores (e.g., alcohol).
  • Low (LLD): Kills most bacteria, some viruses/fungi (e.g., Quats).

• Spaulding's Classification (Item Risk):

  • Critical: Sterile tissue entry. Requires Sterilization. (e.g., surgical tools, implants).
  • Semi-critical: Mucous membrane/non-intact skin contact. Requires HLD. (e.g., endoscopes, RT equipment).
  • Non-critical: Intact skin contact. Requires LLD. (e.g., stethoscopes, BP cuffs).

⭐ Prions are the most resistant infectious agents to standard sterilization methods.

Sterilization and Disinfection - Heat Methods Power

• Dry Heat: Sterilizes by protein denaturation, oxidative damage.
  • Hot Air Oven (HAO):
    • Parameters: 160°C (2 hrs), 170°C (1 hr), 180°C (30 mins).
    • Uses: Glassware, oils, powders, metal instruments (non-cutting).
    • Control: Bacillus atrophaeus spores.
  • Incineration: Complete combustion.
    • Temperature: >800°C.
    • Uses: Biomedical waste, infected materials, carcasses.
• Moist Heat: More effective (latent heat of steam); denatures & coagulates proteins.
  • Autoclave (Steam under pressure):
    • Standard: 121°C, 15 psi pressure, 15-20 mins. Kills spores.
    • Uses: Culture media, surgical instruments, dressings, rubber.

    ⭐ Biological indicator for autoclave efficacy: Geobacillus stearothermophilus spores.

  • Pasteurization: Reduces pathogens, not full sterilization.
    • Methods: Holder (63°C, 30 min), Flash (72°C, 15-20 sec), UHT (135°C, 1-2 sec).
    • Uses: Milk, vaccines, beer.
  • Tyndallization (Fractional Sterilization): Steam at 100°C for 20-30 mins, on 3 successive days.
    • Uses: Heat-sensitive media (e.g., egg/serum based, sugars).
  • Boiling: 100°C for 10-30 mins. Disinfects; kills most vegetative bacteria/viruses. Not reliably sporicidal.

Sterilization and Disinfection - Other Agents Arsenal

• Filtration: Removes microbes. Liquids (sera, drugs) via 0.22 µm filters; air via HEPA.

• Radiation:

  • UV (Non-ionizing): Thymine dimers. Surface/air (OTs). Poor penetration.
  • Ionizing (Gamma, X-rays): Free radicals. Sterilizes disposables, heat-sensitive items.

• Chemical Agents:

  • Alcohols (Ethanol, Isopropanol): 70%. Denature proteins. Skin antisepsis. Not sporicidal.
  • Aldehydes:
    • Formaldehyde: Alkylates. Fumigation. Toxic.
    • Glutaraldehyde (2%): Alkylates. Sterilant (6-10 hrs for spores). Endoscopes.
  • Halogens:
    • Iodine (Povidone-iodine): Oxidizes. Skin antiseptic.
    • Chlorine (Bleach): Oxidizes. Water/surface disinfection.
  • Ethylene Oxide (ETO): Alkylating gas. Heat-sensitive items. Toxic, needs aeration.

    ⭐ ETO gas sterilizes heat-sensitive items (catheters, scopes); sporicidal but toxic, needs aeration.

  • Hydrogen Peroxide ($H_2O_2$): Oxidizing. 3-6% antiseptic; >10% sterilant. Plasma sterilization.
  • Phenols (Lysol): Disrupt membranes. Disinfectant.

Sterilization and Disinfection - Control & Checks

• Monitoring Methods:
  • Physical: Cycle time, temperature, pressure charts/records.
  • Chemical: Indicator tapes (e.g., autoclave tape), Bowie-Dick test (checks pre-vacuum autoclave efficacy).
  • Biological (Spore Tests - definitive validation):
    • Steam/H₂O₂ plasma: Geobacillus stearothermophilus (spores killed at 121°C).
    • Dry heat/Ethylene Oxide (ETO): Bacillus atrophaeus.
    • Radiation: Bacillus pumilus.
• Instrument Specifics: Endoscopes require High-Level Disinfection (HLD) e.g., >2% Glutaraldehyde.
• Biomedical Waste (BMW): Must be decontaminated (autoclaved/incinerated) before final disposal.

⭐ Biological indicators (spore tests) are the most reliable method for verifying sterilization efficacy, considered the gold standard for sterility assurance.

High‑Yield Points - ⚡ Biggest Takeaways

• Autoclave (121°C, 15 psi, 15-20 min) is gold standard sterilization, kills spores.
• Hot air oven (160°C, 2 hours) for dry heat sterilization (glassware, oils, powders).
• Glutaraldehyde (2%) is a high-level disinfectant; chemical sterilant with prolonged contact.
• Ethylene oxide gas sterilizes heat-labile items; toxic, carcinogenic.
• Bacillus stearothermophilus spores are biological indicators for autoclave efficacy.
• Bacillus subtilis spores monitor hot air oven and ethylene oxide efficacy.
• Pasteurization (e.g., HTST 72°C, 15 sec) reduces pathogens, not sterilizing.