Sterilization and Disinfection

• sterilization refers to the destruction of all forms of life, including bacterial spores.
• complete removal of microorganism

  sterilization
• Joseph lister introduced antiseptic surgery using carboxylical acid that is now call phenol
• disinfection refers to a process that eliminates a defined scope of microorganism, including some spores
• physical or chemical method may be used but most disinfectants are chemical agents applied to inanimate objects
• disinfection only reduces the number of microorganism not removing them completely
• antiseptic is a substance applied to skin for the purpose of eliminating or reducing the number of bacteria present
• antiseptic doesn't kill spores and cannot be used as disinfectants
• different organisms have varying ability in withstanding chemical and physical treatment due to different biochemical composition of these organisms and various mechanism that they use to protect themselves
• is a bacteria where spores are coated with proteins, lipids, and carbohydrates as well as dipicolinic acid and calcium

  Spore forming bacteria
• the cell wall is high in lipid which enables them to become resistant to most environmental stress such as desiccation

  myobacterium spp.
• prions is a naked pieces of proteins, similar to viruses, but without nucleic acid, that is most resistant to the action of heat, radiation and chemicals
• prions is an agent that able to cause the generative disease of our nervous system
• the amount of organism present in the object yo be treated referred to as microbi load.

  Number of organisms
• the higher the number of organism, the longer the exposure time needed to eliminate 99.9% of the microorganism
• The amount needed to destroy microorganism varies based on the agent to be used

  concentration of disinfecting agent
• blood, pus, and mucus are examples of organic materials that may prevent full contact of agent to the organic, hence limiting its action

  presence of organic material
• instrument that we use in lab sometimes are made up of biomaterial which exempts them to disinfection or sterilization due to possible damage

  nature of surface to be disinfected
• It is critical to observe proper contact time of the agent and the object to be disinfected or sterilized

  • too little contact time does not allow the agent to work properly

  contact time
• disinfectants are usually used at room temperature (20 to 22°C.)

  • too high to low temp may inactive disinfectants and sterilants


  Temperature
• It is important important consider the pH of the material to be treated and the agent itself.

  • Manufacturers usually optimize this factor to achieve maximum activity

  pH
• certain bacteria have the ability to form communities of layers of bacteria with protective shield called


  biofilm
• biofilm formation may require longer contact time or increase in the concentration of the agent
• some disinfectants may inactivate the action of each other hence it is important to consider the

  compatibility of disinfectants
• autoclave operates based on the principle of steam under pressure.

  • Sterilization: 121 degrees celsius from 15lbs/ in2 for 15mins
  • Decontamination: 135 degrees celcius for 30lbs/in2 for 30mins
• Biological indicator of autoclave is geobacillus stearothermophilus

  • purple indicates nonsterility
  • yellow indicates sterility
• Tyndalization is a fractional discontinuous sterilization and discontinuous heating

  • Effective indication: 100 degree celsius for 30-60minutes
  • Instrument: Arnold's sterilizer
• Inspissation is thickening through evaporation

  • Effective indication: 75-80 degrees celsius for 2 hours
  • Instrument: Inspissator
• Direct heat: direct application of flame in aseptic technique; until red hot
• Dry/Hot air oven: sterilization of heat resistant materials

  • EI: 160-180° C for 1.5 to 2 hours
• Biological Indicator of Dry/Hot Oven: Bacillus atropheus
• Incineration: burns materials into ashes; used in the disposable of biological wastes

  • EI: 870-980° C for 2 seconds
• Ionizing Radiation works by alkylation of nucleic acid of bacteria using high energy short wavelength deep penetrating gamma rays

  • used for heat sensitive materials
• biological indicator of ionizing radiation: Bacillus Pumilis
• Filtration used membrane filters that are usually made of plastic polymers or cellulose esters that contains pores
• Filtration

  Water/ liquid solutions/ antibiotics/ vaccines

  • usually uses a thin membrane filter of cellulose acetate with different pore size depending on the intended purpose
• Filtration

  Water/ liquid solution/ antibiotics/ vaccines:

  • 0.45-0.80 Mm - most bacteria, yeast, and molds are retained but may allow passage of Pseudomonas like organisms.
• Filtration Water/ liquid solution/ antibiotics/ vaccines

  • 0.22 Mm - used to filter Pseudomonslike organisms; used for critical sterilization of parental solutions
• Filtration

  Water/ liquid solution/ antibiotics/ vaccines:

  • 0.01 Mm - able to retain small viruses
• Filtration

  Air: High Efficiency Particulate Filte (HEPA)

  • has a pore size of 0.03Mm; usually used in biological safety cabinet and rooms of immunocompromised patients