Sterilization and disinfections


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Sterilization and disinfections

  2. 2.  Sterilization: is defined as the process where all the living microorganisms, including bacterial spores are killed. Disinfection: is the process of elimination of most pathogenic microorganisms (excluding bacterial spores) on inanimate objects. Chemicals used in disinfection are called disinfectants. Sterilization is an absolute condition while disinfection is not.
  3. 3. METHODS OF STERILIZATION: The various methods of sterilization are:1- Physical Methods: a. Radiation method . b. Filtration method . c. Thermal (Heat) methods: I- Dry Heat. II- Moist Heat.2- Chemical Method: By using chemicals.
  4. 4. 1- PHYSICAL METHODS OF STERILIZATION: a. Radiation: Since radiation does not generate heat, it is termed "cold sterilization". In some parts of Europe, fruits and vegetables are irradiated to increase their shelf life up to 500 percent. Two types of radiation are used, ionizing and non-ionizing.
  5. 5. I- Non-ionizing rays: Non-ionizing rays are low energy rays with poor penetrative power and with wavelength longer than the visible light. Mechanism of action:1- UV rays inhibits DNA replication.2- Since UV rays don’t kill spores, they are considered to be of use in surface disinfection.
  6. 6.  Advantages: UV rays are employed to disinfect hospital wards, operation theatres, virus laboratories, corridors, etc. Disadvantages:1- low penetrative power.2- Organic matter and dust prevents its reach.3- Rays are harmful to skin and eyes.4- It doesnt penetrate glass, paper or plastic.
  7. 7. II- Ionizing rays: ionizing rays are high-energy rays with good penetrative power . These high-energy radiations damage the nucleic acid of the microorganism which kill all bacteria, fungi, viruses and spores. It is used commercially to sterilize disposable petri dishes, plastic syringes, antibiotics, vitamins, hormones, glasswares and fabrics. Examples: X- rays, Gamma rays.
  8. 8. b- Filtration Sterilization : Filtration process does not destroy but removes the microorganisms. Used in the treatment of heat sensitive injections and ophthalmic solutions, biological products and air and other gases for supply to aseptic areas. Application of filtration for sterilization of gases: HEPA (High efficiency particulate air) used in Laminar air flow cabinets.
  9. 9.  There are two types of filters used in filtration sterilization:(a) Depth filters: They are made of diatomaceous earth, unglazed porcelain filter, sintered glass or asbestos.(b) Membrane filters: These are porous membrane made of cellulose acetate, polycarbonate or some other synthetic material.Fluids are made to transverse membranes by positive or negative pressure or by centrifugation.
  10. 10. c- Heat: I- Dry Heat: Heat sterilization is the most widely used and reliable method of sterilization, involving destruction of enzymes and other essential cell constituents. Thismethod of sterilization can be applied only to the thermostable products.
  11. 11. 1- Red heat:By holding articles in Bunsen flame till they become red hot (bacteriological loops, straight wires)2- Flaming: This is a method of passing the article over a Bunsen flame, but not heating it to redness (scalpels, mouth of test tubes, flasks, glass slides). Even though most vegetative cells are killed, there is no guarantee that spores too would die on such short exposure.
  12. 12. 3- HOT AIR OVEN: Used for sterilizing materials that must remain dry e.g. antibiotic powders Hot air circulating ovens are used for this purpose. Articles sterilized: Metallic instruments (like forceps, scalpels, scissors) glasswares (such as petri-dishes, pipettes, flasks, all- glass syringes), and some pharmaceutical products. A temperature of 160-170oC for 2-3 hours is used commonly. Precautions: 1- Articles to be sterilized must be perfectly dry before placing them inside to avoid breakage. 2- The hot air oven must not be opened until the temperature inside has fallen below 60oC to prevent breakage of glasswares.
  13. 13.  Advantages:1- It is an effective method of sterilization of heat stable articles. The articles remain dry after sterilization.2- This is the only method of sterilizing oils and powders. Disadvantages:1- Since air is poor conductor of heat, hot air has poor penetration.2- Cotton wool and paper may get slightly charred.3- Glasses may become smoky.4- Takes longer time compared to autoclave.