Methods of Sterilization in Microbiology

Sterilization

• The process of eliminating transmissible agents from surfaces, equipment, foods, medications or biological culture media.

Methods of Sterilization

• Physical: Thermal (heat), radiation, filtration
• Chemical: Gaseous

Physical Methods: Heat

• Heat is the most widely used and reliable sterilization method.
• Dry Heat: 160-180°C for up to 2 hours, for thermo stable products (glassware, metal surgical instruments, non-aqueous thermo stable liquids and powders).
• Moist Heat: 121-134°C using steam under pressure, for moisture-resistant materials and is the most dependable method for decontamination of laboratory waste and sterilization of laboratory glassware, media, and reagents.
• Autoclave: uses pressurized steam to destroy microorganisms.

Thermal (Heat) Methods

• Thermal methods include:
  • Dry Heat Sterilization:
    • Flaming, incineration, hot air oven
  • Moist Heat Sterilization:
    • Boiling water/ steam at atmospheric pressure
    • Hot medium below boiling point (Pasteurization)
    • Dry saturated steam – Autoclaving

Dry Heat

• Employ higher temperatures (160-180°C) and requires an exposure time of up to 2 hours.
• Benefits include good penetrability and non-corrosive nature.
• Destroys bacterial endotoxins.

Moist Heat

• Uses steam in the range of 121-134°C.
• Saturated steam is an effective sterilizing agent.

Radiation Sterilization

• Uses ionizing radiation (gamma or X-rays) to destroy microorganisms by damaging their DNA.
• Non-ionizing radiation (UV light) is used for surface sterilization.
• Advantages include:
  • No degradation of media during sterilization.
  • Leaves no chemical residue.
  • Precise and uniform dosage distribution.
  • Immediate availability of media after sterilization.
• Disadvantages:
  • More costly than heat sterilization.
  • Requires specialized equipment.

Filtration Sterilization

• Removes microorganisms and does not destroy them.
• Used for both clarification and sterilization of liquids and gases.
• Major mechanisms: sieving, adsorption, trapping within the filter material.
• Employed for heat sensitive injections and ophthalmic solutions, biological products, and air and other gases for supply to aseptic areas.
• Types:
  • Depth filters use a porous filtration medium to retain particles throughout the media.
  • Membrane filters are porous membranes made of cellulose acetate, cellulose nitrate, polycarbonate, polyvinylidene fluoride, or some other synthetic materials.

Chemical Sterilization Method

Gaseous Method

• Chemically reactive gases like formaldehyde and ethylene oxide possess biocidal activity.
• Mechanism of action is through alkylation of proteins and nucleic acids.
• Ethylene oxide is commonly used to process heat-sensitive devices.
• Both gases are potentially mutagenic and carcinogenic and produce acute toxicity.

Liquid Sterilization

• Involves submerging equipment in a liquid sterilant to kill all viable microorganisms and their spores.
• Not as effective as gaseous sterilization, but appropriate for low contamination levels.

Importance of Sterilization

• Moist heat sterilization is the most efficient biocidal agent, commonly used for many items.

Explore the various methods of sterilization used in microbiological practices. Learn about physical methods like dry and moist heat, as well as chemical methods. This quiz covers the principles and applications of these essential sterilization techniques.