sterilization

• Sterilization


  The process of eliminating/removing of all microorganisms and all of their active living forms (including bacteria, bacterial spores, viruses, fungi and parasites)
• Disinfection


  The process of eliminating disease causing microorganisms from an object
• Antisepsis


  The practice of cleaning of surface tissues of human body (skin, mucosa) and lesions (wounds) to eliminate disease-causing microorganisms
• Hospital-acquired infections represent an important healthcare problem for patients, healthcare workers, the community and healthcare budget
• Hospital-acquired infections can lead to increase in morbidity and mortality, loss of efficiency in hospitals and medical institutions, and major increase in costs
• According to data from Centers for Disease Control (CDC), 30% of hospital-acquired infections can be prevented when main sterilization and disinfection rules are applied
• This also applies to surgical infections where prevention rate can be 19-41%
• Microorganisms


  When in appropriate environment, like all other living things, can be nourished and grow. They exist in soil, air, human body and in all environments
• Microorganisms should be removed during medical and surgical operations, from tools and media used for identification of microorganisms, and from drinking water, consumed food and drinks
• Cleaning


  Removal of foreign material (soil, organic material, microorganisms etc) from an object and substance
• Decontamination


  Removal of contaminating microorganisms from a substance in order to be safely used
• Sterile


  When sterilization is applied to a material, that material is referred to as sterile
• Disinfectant


  Chemicals used out of the human body for disinfection (e.g. Floor, clothing, hospital tools)
• Antiseptic


  All the chemicals used for disinfection of body and tissues
• Asepsis


  All the measures taken for the prevention of microbial contamination in wounds and environment
• Aseptic


  An environment, wound etc. where all asepsis measures are taken
• Pasteurization


  The method of heat processing for the disinfection of mostly milk or milk products
• Generally for milk; 30 minutes at 62ºC, 15 seconds at 72ºC or 3-5 seconds at 135-150ºC (Very high temperatures (UHT) and cooled down quickly
• Microbicide (germicide)


  The effect of prevention of growth and multiplication and killing of microorganisms (bactericide, virucide, fungicide, sporocide, tuberculocide)
• Microbiostatic


  Prevention/inhibition of the growth/multiplication of microorganisms
• Resistance patterns of microorganisms to sterilization and disinfection

  • Prions
  • Bacterial spores
  • Mycobacteria
  • Parasite cysts
  • Small, non-enveloped viruses
  • Trophozoites
  • Gram negative bacteria
  • Fungi
  • Large, non-enveloped viruses
  • Gram positive bacteria
  • Enveloped viruses
• Spaulding classification


  The level of terminal reprocessing required by medical devices is based on the classification system developed by Spaulding in 1970. It divides medical devices into 3 categories, based on the client/patient/resident's risk of infection
• Heat sterilization


  Among all sterilization techniques, heat is the most reliable, most economical, least toxic, and easiest to apply. The material being sterilized needs to be heat-resistant
• Mechanism of action of heat sterilization

  Coagulation of proteins of the cell
• Factors important for heat sterilization

  • Time (more time, more effective)
  • Temperature (the higher temperature, the shorter time)
  • pH (heat effect increases as pH changes from neutral)
  • Moisture content (the more moisture, more effect of the heat)
  • Osmotic pressure (of high, microorganisms can reduce water content)
• Moist heat sterilization


  Water at high pressure level is used for moist heat sterilization. Pressurized vapour sterilization (autoclave) and Non-pressure vapour sterilization (Koch's sterilizer)
• Pressured vapour sterilization (autoclave)


  The most effective and reliable sterilization technique. Invented by Charles Chamberland in 1879. Autoclave consists of a vertical or a horizontal cylinder with an opening for keeping materials to be sterilized. The lid is provided with a pressure gauge to measure the pressure. A safety valve is present to permit the escape of steam from the chamber
• Fundamental principle of autoclave

  The saturated steam under pressure has a temperature higher than the boiling temperature of water. The latent heat which condenses is transferred to the objects and moist heat kills the microorganisms very quickly
• Recommended temperatures and timing for autoclave

  • 115ºC for 30 minutes
  • 121ºC for 15 minutes (15-45)
  • 134ºC for 3 minutes (flash sterilization) for normal autoclave
  • 134ºC for 60 minutes for samples with suspected prion
  • 134ºC for 18 minutes, 121ºC for 60 minutes for vacuum autoclave
• Objects that can be sterilized in autoclave

  • Rubber Materials
  • Media
  • Liquids etc.
• Objects that cannot be sterilized in autoclave

  • Powder
  • Oils
• Important points while using the autoclave for sterilization

  • Bottles or containers should be packaged so that moisture can penetrate
  • Containers should not be placed too tightly
  • Large surfaces of containers should be horizontal
  • All capped-bottles should be left slightly loose
  • Objects contaminated with microbes should be autoclaved separately
  • All the air should be removed from the objects or packages during the sterilization
• Non-pressured vapour sterilization (Koch's sterilizer)

  Sterilization by saturated and non-pressurized vapor at 100ºC. Duration of sterilization: 30 minutes after reaching 100ºC. Not commonly used today, maybe used for heat sensitive items e.g. saccharide solution
• Sterilization by hot water boiling

  100ºC for 30 minutes boiling (time should be calculated after starting to boil). For materials sensitive to too high temperatures. Boiling is used for sterilization of glass and metals. This technique should be used in the first step healthcare services if no autoclave is present
• Tyndallization


  Involves heating to 56-100ºC for consecutive 3 days for 1 hour. Liquid materials sensitive to high temperatures can be treated with this technique. Serum (protein containing) 56ºC, Solutions that can be hydrolyzed 70ºC, Vaccines and saccharide solutions 100ºC. Benmari is used for this sterilization technique
• Inspissator


  Sterilizes by heating at 80-85°C for half an hour for 3 successive days. Used to sterilize media such as Lowenstein-Jensen & Loefller's serum
• Boiling at 100°C kills vegetative forms of bacterial pathogens. Hepatitis virus can survive up to 30 minutes of boiling. Endospores can survive up to 20 hours or more of boiling
• Sterilization by dry hot air

  There is the need for higher temperatures and longer timing as there is no moisture. Pasteur oven is used. In the oven, the transport of microorganism is via the substances that heat up rather than the hot water. Therefore, materials which conduct heat better are sterilized much easier. It is less reliable
• Recommended sterilization times for Pasteur oven

  • 180ºC for 0.5h
  • 170ºC for 1h
  • 160ºC for 2h
  • 150ºC for 2.5h
  • 140ºC for 3h
• Objects that can be sterilized in Pasteur oven

  • Glass tools (petri dish, pipets, tubes)
  • Metal tools (scissors)
  • Powder and oils (to which moisture cannot reach and therefore cannot be autoclaved) e.g. Vaseline, paraffin