Lesson 2

• Sterilization


  (Latin sterilis – unable to produce offspring or barren) is the process by which all living cells, viable spores, viruses, and viroids are either destroyed or removed from an object or habitat, and achieved by physical means and chemical means
• Sterilant


  A chemical agent used to achieve sterilization
• Disinfection


  The killing, inhibition, or removal of microorganisms that may cause disease; the primary goal is to destroy potential pathogens, but disinfection substantially reduces the total microbial population
• Disinfectants


  Agents, usually chemical, used to carry out disinfection and are normally used only on inanimate objects
• Germicide


  A suffix can be employed to denote the type of antimicrobial agent. Substances that can kill organisms often have the suffix – cide (Latin cida, to kill) kill pathogens (and many non-pathogens) but not necessarily endospores
• A larger population


  Requires a longer time to die than a smaller one
• Conditions influencing the effectiveness of antimicrobial agent activity

  • Population Composition
  • Concentration or Intensity of an Antimicrobial Agent
  • Duration of Exposure
  • Temperature
  • Local Environment
• Heating


  Fire and boiling water have been used for sterilization and disinfection since the time of the Greeks, and heating is still one of the most popular ways to destroy microorganisms
• Types of heat

  • Moist Heat
  • Dry Heat
• Moist Heat - Temperature below 100-degree Celsius


  • Pasteurization
  • Vaccine Bath
  • Serum Bath
  • Inspissation
• Pasteurization


  Many substances, such as milk, are treated with controlled heating at temperatures well below boiling point. (developed by Louis Pasteur)
• Types of Pasteurization

  • Flash pasteurization / high temperature short term (HTST) pasteurization
  • Ultrahigh-temperature (UHT) sterilization
• Flash pasteurization / high temperature short term (HTST) pasteurization


  Quick heating to about 72 degree C for 15 seconds, then rapid cooling
• Ultrahigh-temperature (UHT) sterilization


  Heated 140 to 150 degrees C for 1 to 3 seconds; does not require refrigeration, (room temperature) for about 2 months without flavor changes
• Vaccine Bath


  This is used to destroy contaminating bacteria in vaccine preparations; heated in a water bath at 60 ° C for one hour daily in a vaccine bath for several successive days; only vegetative forms of the bacteria are destroyed
• Serum Bath


  Used to inactivate bacteria contaminating serum preparations; heating at 56°C for several successive days; similar to vaccine bath, only the vegetative forms are destroyed since higher temperatures will cause coagulation of proteins present in the serum
• Inspissation


  Used to solidify and disinfect egg-containing and serum-containing bacteria; heated at 80°C -85°C for 30 minutes for three successive days
• Moist Heat - Temperature at 100-degree Celsius


  • Boiling
  • Fractional Sterilization (Tyndallization)
• Boiling


  Involves utilizing water at a boiling temperature of 100°C; it is not sporicidal; only destroys vegetative forms; certain metal articles and glassware can be disinfected using this method for 10-20 minutes without opening the lid of the boiler
• Fractional Sterilization (Tyndallization)


  Intermittent sterilization; live steam at 100°C for 30-90 minutes for three consecutive days (depending on the material to be sterilized); sterilized culture media and selenite broth
• Moist Heat - Temperature above 100-degree Celsius


  Steam Sterilization
• Steam Sterilization


  Moist heat sterilization must be carried out at temperatures 100 degrees C to destroy bacterial endospores, and this requires the use of saturated steam under pressure; steam sterilization is carried out with an autoclave, a device somewhat like a fancy pressure cooker; usually, 121 degrees C and 15 pounds of pressure
• Dry Heat


  • Open Flame
  • Red Flame
  • Incineration
  • Hot Air Oven
  • Infrared Rays
  • Desiccation
  • Freezing
  • Filtration
  • Radiation
  • Sonic and Ultrasonic Vibrations
  • Osmotic Pressure
• Red Flame


  This method is used to sterilize articles like bacteriological wire loops, straight wires, tips of forceps, and searing spatulas; the materials are held over the flame of a Bunsen burner until they become red-hot
• Open Flame


  Also makes use of the Bunsen burner or alcohol lamp; material sterilized is passed over the flame several times but is not heated to redness; aimed at burning the organism into ashes and is used to sterilize articles as mouths of test tubes, scalpels, glass slides, and cover slips; cracking of the glassware may occur
• Incineration


  Aimed at burning the organism into ashes; the contaminated material is burned using an incinerator; articles incinerated include soiled dressings and beddings, animal carcasses, and pathological material; used only for articles that have to be disposed
• Hot Air Oven


  Introduced by Louis Pasteur; articles are placed in the oven at a temperature of 160°C for one hour; it can be used to sterilize certain glassware (e.g., Petri dishes, pipettes, and flasks); and the only method used to sterilize powders and ointments; disadvantages: poor conductor of heat; wool and paper slightly charred and glasses can become smoky
• Infrared Rays


  Articles to be sterilized are placed in a conveyor belt and passed through a tunnel that is heated by infrared radiators; the temperature is 180 °C for 7.5 minutes; sterilize metallic equipment and glassware
• Desiccation


  This method is based on the principle of depriving the microorganisms of moisture; it is used mainly for food preservation, such as in the preparation of dried fish and fruits; it destroys vegetative forms; endospores are resistant to drying
• Freezing


  Inhibits microbial growth and reproduction by low temperature and absence of liquid water
• Filtration


  Removes contaminating microorganisms without directly destroying them; sterilizes heat-sensitive materials
• HEPA Filters (Air)


  • Used in operating rooms and burn units to remove bacteria from the air
• Membrane Filters (Liquids)


  • Porous membranes made of various synthetic materials, replace depth filters for many purposes
• Ultraviolet Light (UVL) / Non-ionizing Radiation


  Effective wavelength is 200 nm - 280 nm, with 260 nm as the most effective; can inactivate microorganisms like bacteria, viruses, and yeasts within seconds
• Ionizing Radiation


  Greater penetrance than UV rays; causes formation of free radicals that chemically interact with proteins and nucleic acids, resulting in cell death
• Electron Beams


  • Generated by a linear accelerator, can be used to sterilize various items
• Electromagnetic (Gamma Rays)


  • Greater penetrance than electron beams but requires longer exposure time
• Sonic and Ultrasonic Vibrations


  Can kill some bacteria and viruses after exposure to certain frequencies
• Osmotic Pressure


  Based on the principle of Osmosis; creating a hypertonic environment (high concentration of salts and sugar)
• Surface Active Agents (Surfactants)


  Long-chain hydrocarbons that are fat-soluble and charged ions that are water-soluble