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).