Microbial Control Methods

HOW CLEAN IS "CLEAN"?

  • Most environments, including cars, are not sterile.
  • A study analyzed 11 locations in 18 different cars for microbial colonies.
    • The center console had the highest microbes, 506 CFUs, possibly due to drinks.
    • Frequently touched areas also had high concentrations.

CONTROL OF MICROBIAL GROWTH

  • Selection of Antimicrobial Procedure:

    • No ideal method exists; each has drawbacks.
    • Choice depends on:
    • Type of microbes
    • Number of microbes
    • Environmental conditions
    • Infection risk
    • Composition of the infected item

  • Autoclaving:

    • Gold standard for sterilization, effectively sterilizes most microbes when done properly.

COMMON PROTOCOLS FOR CONTROL OF MICROBIAL GROWTH

  • Definitions:

    • Disinfection: Reduces or destroys microbial load through heat or chemicals.
    • Sanitization: Reduces microbial load to safe levels for public health.
    • Sterilization: Completely eliminates all cells and viruses.

  • For Living Tissue:

    • Antisepsis: Reduces microbial load on skin.
    • Degerming: Involves scrubbing and mild chemicals.

TERMINOLOGY

  • Suffixes:
    • -static: inhibits growth
    • -cide: kills/inactivates
  • Prefixes:
    • Fungi-: fungi (yeast, mold)
    • Bacteri-: bacteria
    • Viri-: viruses

PHYSICAL METHODS OF MICROBIAL CONTROL

  1. Heat:

    • Moist Heat:
      • Boiling: 100°C, denatures proteins, does not kill endospores.
      • Autoclaving: 121°C for 20 mins at 15 psi, kills endospores.
    • Dry Heat:
      • Incineration: destroys by burning.
      • Heat in oven: 170°C for 2 hours.

  2. Cold:

    • Refrigeration (0-7°C) slows growth, freezer (-20°C) delays spoilage.
    • Ultra-low temperature freezers (-70°C) can store cultures long-term.

  3. Pressure:

    • High-pressure processing denatures proteins, killing microbes, but may not kill endospores.
    • Used to maintain food quality and extend shelf life.

  4. Desiccation:

    • Removing water creates hypertonic environments, leading to microbial death.
    • Lyophilization: freeze-drying process.

  5. Radiation:

    • Ionizing Radiation: Gamma rays, X-rays, break down DNA.
    • Non-ionizing Radiation: UV light, causes DNA mutations (thymine dimers).

  6. Filtration:

    • HEPA Filters: remove microbes from air.
    • Membrane Filters: various pore sizes for liquid filtration.

GERMICIDAL CHEMICALS

  • Common Chemicals:
    • Alcohols: Easy to use but evaporate quickly.
    • Aldehydes: Effective but toxic; used for instruments.
    • Halogens: Inexpensive but can react with organic compounds.
    • Phenolic Compounds: Effective against a wide range, but some may have toxic effects.

DECIMAL REDUCTION TIME (D-value)

  • Microbial death observed logarithmically.
  • D-value: Time to kill 90% of a population under specific conditions.

DISK DIFFUSION ASSAY

  • Used to test chemical effectiveness against microbes.
    • Zone of inhibition indicates effectiveness.

HANDWASHING

  • One of the simplest and most effective methods for reducing microbial load.
    • Important in both general and surgical settings.

BIOSAFETY LEVELS

  • Classified into four levels based on risk to personnel and the public:
    • BSL-4: Dangerous/exotic microbes, high transmission risk (e.g., Ebola).
    • BSL-3: Serious diseases, respiratory risks (e.g., tuberculosis).
    • BSL-2: Moderate risk diseases (e.g., Staphylococcus aureus).
    • BSL-1: Minimal risk microbes, do not cause disease (e.g., non-pathogenic E. coli).