Introduction to Sterilization

Introduction to Sterilization

• Sterilization is the complete elimination of all living microorganisms, including spores, from a product.
• Sterilization ensures a product is sterile or non-sterile, there is no in-between.
• Different sterilization methods are needed depending on the product and contaminant.

Factors Affecting Sterilization Process

• The success of sterilization depends on the chosen temperature and duration of exposure.
• High temperatures can damage the product, which can reduce its effectiveness, stability, or patient acceptability.
• A suitable sterilization process balances the risk of failing to achieve sterility with the risk of product damage.

Selection of Sterilization Method

• The most suitable sterilization method depends on the properties of the product, sterilizing agent, and contaminant.

Kinetics of Microbial Death

• Bacterial death is defined as the inability to multiply, not the lack of active metabolism.
• Microbial death occurs logarithmically, meaning the rate of killing is proportional to the initial number of viable cells.

Survivor Curve

• Survivor curves plot the logarithm of surviving microorganisms against time.
• There are three phases:
  • Initial Lag Phase: Diffusion of the killing agent into the cells, or germination of spores.
  • Exponential Phase: Linear decrease of viable cells.
  • Final Tailing: Presence of resistant cells or mutants.

Expression of Resistance to Sterilization

• Thermal Death Point (TDP): The lowest temperature required to kill all microorganisms in a suspension within a specific time (usually 10 minutes).
• Thermal Death Time (TDT): The shortest time required to kill all microorganisms in a suspension at a specific temperature.
• Decimal Reduction Time (D-value): Time at a fixed temperature or radiation dose needed to reduce the number of viable cells by 90% (one log cycle).
• Z-value: The increase in temperature required to reduce the D-value of an organism by 90% (one log cycle).

Heat Sterilization

• Each microorganism has an optimal temperature for growth.
  • Growth decreases reversibly below the optimal temperature.
  • Growth decreases irreversibly above the optimal temperature.
  • This is because heat degrades vital molecules.
• The Higuchi and Busse equation describes the effect of heat on microbial death:
  • log t = 0.219 E + K
    • t = extinction time
    • T = absolute temperature
    • K = constant depends on the number and type of microorganisms
    • E = heat of activation energy required to kill the most resistant microorganism
• Plotting log t against T results in a straight line.

Sterilization Methods

• Physical Sterilization

  • Heat Sterilization:
    • Dry Heat: Sterilization using dry heat, often at high temperatures.
    • Moist Heat: Sterilization using steam or water.
  • Radiation Sterilization: Sterilization using ionizing radiation or ultraviolet light.
  • Filtration Sterilization: Sterilization using filters to remove microorganisms from solution.

• Chemical Sterilization:

  • Gaseous Sterilization: Using gases like ethylene oxide or hydrogen peroxide for sterilization.
  • Heating with Bactericides: Using heat to enhance the action of chemical bactericides

This quiz covers the fundamentals of sterilization, including its definition, methods, and factors affecting the sterilization process. Participants will explore the kinetics of microbial death and how to choose suitable sterilization methods for various products. Test your knowledge on these essential concepts in sterilization.