Sterilization and Disinfection in Microbiology

Title: Sterilization and Disinfection in Microbiology

Author: Dr. Hassan Abul

Terminologies

• Disinfection:

  • Killing or removing harmful microorganisms.

  • Kills vegetative cells but not spores.

• Sterilization:

  • Process used to kill all forms of microorganisms and spores.

• Disinfectant:

  • Product applied directly to inanimate objects.

• Sanitizers:

  • Product used to reduce the number of microorganisms on surfaces to levels considered safe from a public health standpoint.

• Antiseptics:

  • Chemical disinfectants used to prevent infection by inhibiting growth of bacteria.

Difference Between Disinfectant and Sterilization

Disinfection

• Lowers the number of harmful microbes to an acceptable level.

• Kills vegetative cells but not spores.

• Examples of use: Wounds disinfected with hydrogen peroxide or alcohol.

• Methods include chemical processes.

• Commonly used in daily life.

Sterilization

• Completely free from all microbes.

• Kills both vegetative cells and spores.

• Wounds cannot be sterilized as it may kill surrounding healthy cells.

• Methods include heat, irradiation, high pressure, chemical, and physical methods.

• Primarily used for medical and research purposes.

Basic Terminologies

• Bactericidal agents:

  • Kill bacteria.

• Bacteriostatic agents:

  • Inhibit multiplication of bacteria.

• Biocide:

  • Chemical agents that kill microorganisms, e.g., disinfectants, antiseptics, antibiotics.

• Decontamination:

  • Process of removing contaminants, including microbial, chemical, and radioactive hazards.

Methods of Sterilization/Disinfection

Sunlight

• Action is primarily due to ultraviolet (UV) rays.

• Not effective against spores.

Heat

• Most reliable method of sterilization.

• Factors influencing effectiveness:

  • Environment (dry or moist).

  • Temperature and time.

  • Number and type of microorganisms.

Methods of Sterilization/Disinfection - Dry Heat

Flaming

• Object is passed over a Bunsen burner or flame; used for scalpels, flasks, loops.

Incineration

• Destroys contaminated materials by burning in an incinerator.

Hot Air Oven

• Most common method for sterilization by dry heat (e.g., glassware, forceps, swabs).

  • Precautions include:

    • Glassware must be dry.

    • Oven shouldn't be overloaded.

    • Cool down before opening.

Methods of Sterilization/Disinfection - Moist Heat

• Temperature below 100°C: Pasteurization of milk; targets all non-sporing pathogens.

• Temperature at 100°C: Boiling; not recommended for sterilization but used for disinfection.

• Temperature above 100°C: Autoclave/steam sterilizer; kills all types of bacteria, viruses, fungi; ideal for lab glassware.

Methods of Sterilization/Disinfection - Filtration

• Removes bacteria from heat-labile liquids.

• Principle: Viruses pass through filters to obtain bacteria-free filtrates.

Methods of Sterilization/Disinfection - Radiation

Non-Ionizing Radiation

• Infrared: Used for rapid mass sterilization of prepacked items (e.g., syringes, catheters).

• Ultraviolet (UV): Used for disinfecting enclosed areas (e.g., laminar flow cabinets).

Ionizing Radiation

• Gamma rays and X-rays: Used for sterilizing plastics, swabs, catheters, and syringes.

Methods of Sterilization/Disinfection - Chemical

Liquid

• Alcohol: Ethyl and isopropyl alcohol (concentration of 60-90%); methyl alcohol effective against fungal spores.

• Aldehyde: Formaldehyde has bactericidal effects on bacteria and is effective against viruses.

• Dyes: Aniline and acridine dyes; bacteriostatic in high dilutions.

• Phenols: Cause cell membrane damage leading to cell lysis.

Gases

• Ethylene oxide: Alkylates protein molecules.

• Formaldehyde gas: Used for fumigation.

• Beta-propiolactone: Bactericidal but carcinogenic.

Methods of Sterilization/Disinfection - Indicators

Mechanical Indicators

• Part of autoclave or dry heat oven; tracks time, temperature, and pressure during sterilization cycle.

Chemical Indicators

• Tape with lines to ensure intended temperature was achieved.

Biological Indicators

• Use heat-resistant bacterial endospores to demonstrate sterilization efficacy (if endospores are killed, all microorganisms are assumed killed).

Ideal Characteristics of Antiseptics/Disinfectants

• Effective against all microorganisms.

• Effective in both acid and alkaline media.

• Rapid action.

• High penetrating power.

• Stable and non-corrosive to metals.

• Non-irritating and interferes minimally with healing.

• Inexpensive and easily available.

• Compatible with other antiseptics and disinfectants.