Disinfection and Sterilization

Disinfection and Sterilization

Introduction

Disinfection and sterilization are essential procedures in microbiology, medicine, and laboratory sciences. They are used to eliminate or reduce microbial contamination, ensuring safety in healthcare settings, laboratories, and industries such as food, pharmaceuticals, and water treatment.

• Sterilization: The complete destruction or removal of all forms of microbial life, including bacterial spores.
• Disinfection: The process of eliminating or reducing pathogenic microorganisms, except bacterial spores, on inanimate objects.

These processes are vital in preventing healthcare-associated infections (HAIs), laboratory contamination, and cross-infection.

Differences Between Sterilization and Disinfection

Types of Sterilisation

A. Physical Methods

1. Moist Heat Sterilisation (Autoclaving)
• Uses steam under pressure (121°C for 15–20 minutes at 15 psi)
• Kills all microorganisms and spores
• Used for: Culture media, surgical instruments, lab waste
• Indicator: Autoclave tape, biological indicators (e.g., Bacillus stearothermophilus spores)
2. Dry Heat Sterilisation
• Hot air oven (160–180°C for 1–2 hours)
• Destroys microbes by oxidation
• Used for: Glassware, powders, oils, metal instruments
3. Flaming and Incineration
• Flaming: Direct exposure to flame (e.g., inoculating loops)
• Incineration: Burning waste to ashes (used in hospital waste disposal)
4. Filtration
• Removes microbes from heat-sensitive liquids
• Uses membrane filters (0.22 µm pore size)
• Used for: Vaccines, antibiotics, serum
5. Radiation
• Ionising radiation (gamma rays, X-rays): Penetrates deeply, kills all microbes
• Used for: Sterilising disposable medical equipment, food
• Non-ionising radiation (UV light): Surface sterilisation; damages DNA

B. Chemical Methods of Sterilisation

1. Ethylene oxide gas
• Alkylates DNA and proteins
• Used for: Heat-sensitive medical devices (e.g., catheters, syringes)
• Toxic and flammable – requires aeration
2. Formaldehyde gas or solution (formalin)
• Cross-links proteins and DNA
• Used for: Room fumigation, biological specimens
3. Hydrogen peroxide plasma
• Low-temperature method
• Used for: Endoscopes, surgical tools

Types of Disinfection

Disinfection can be high-level, intermediate-level, or low-level, depending on the type and concentration of the chemical used.

Common Disinfectants and Their Uses

Factors Affecting the Efficiency of Disinfection and Sterilisation

• Type and number of microorganisms
• Presence of organic matter (e.g., blood, pus)
• Contact time
• Concentration and potency of the agent
• Temperature and pH
• Surface and material type
• Biofilm formation can reduce effectiveness

Indicators for Monitoring Sterilisation

Applications in Medical Laboratory Science

• Sterilisation of culture media, glassware, instruments
• Disinfection of workbenches, centrifuges, biosafety cabinets
• Autoclaving infectious waste
• Use of antiseptics before sample collection
• Sterile technique during sample processing and diagnostics

Safety Precautions

• Use protective clothing when handling disinfectants
• Use correct concentrations and exposure times
• Avoid mixing chemicals (e.g., bleach and ammonia)
• Ensure proper ventilation during fumigation or gas sterilisation
• Handle sterilised equipment aseptically to avoid recontamination

Summary Table: Sterilisation vs Disinfection