Sterilization and Disinfection Flashcards
what is sterilization?
sterilization is the killing or removal of all microorganisms including bacterial spores which are highly resistant.
what is disinfection?
disinfection is the killing of many, but it all, microorganisms. For adequate disinfection, pathogens must be killed but some organisms and bacterial spores may survive.
what are antiseptics?
chemicals used to kill microorganisms on the surface of the skin and mucous membranes
what are the three mechanisms by which chemical/physical agents act primarily?
- disruption of the lipid-containing cell membrane
- modification of proteins
- modification of microbial DNA
what are the types of sterilization/disinfection due to disruption of cell membranes?
- alcohol: ethanol is widely used to clean the skin before immunization or venipuncture (antiseptic). It acts by disorganizing the lipid structure in membranes and denatures proteins as well. It is more effective at 70% than at 100%.
- detergents: benzalkonium chloride is one of the active ingredients in detergents and it is widely used for skin antisepsis.
- phenols: cresol is the active ingredient in lysol. Phenols damage membranes and denature proteins.
why is ethanol more effective at 70% than at 100%
Ethanol requires the presence of water for maximal activity
what does 100% ethanol cause?
skin irritation and rashes
what are the types of sterilization/disinfection due to modification of proteins ?
- chlorine: used as a disinfectant to purify water supply and to treat swimming pools. It is also the active component of hypochlorite (bleach) which is used as a disinfectant in the home and hospitals.
- iodine: most effective skin antiseptic used in the medical practice and should be used prior to obtaining a blood culture and installing intravenous catheters
- heavy metals: mercury and silver have the greatest antibacterial activity of the heavy metals and are the most widely used in medicine (skin antiseptics). Silver nitrate drops are used to prevent gonococcal ophthalmia neonatorum and silver sulfadiazine is used to prevent infection of burn wounds
- hydrogen peroxide: used as an antiseptic to clean wounds and to disinfect contact lenses
- ethylene oxide: one of the best sterilization techniques. It is used extensively in hospitals for the sterilization of heat-sensitive materials such as surgical instruments and plastics. Conducted at 30/40/50° C for a period of 3-4 hours
- acids and alkalis: weak acids such as benzoic, propionic, citric acids are used as food preservatives
what are the physical agents of sterilization/ disinfection?
- autoclave: moist-heat sterilization. Most frequent method of sterilization because bacterial spores are resistant to boiling (100° C). Autoclave at a pressure of 15 lb/in2, temperature of 121° C and time period of 15-20 minutes. This kills even the highly resistant spores of Clostridium botulinum.
- pasteurization: used primarily for milk. Consists of heating milk to 62° C for 30 minutes followed by rapid cooling OR flash pasteurization- heating milk at 72° C for 15 seconds OR ultra high temperature- heating milk at 90° C for 3-5 seconds. This does not sterilize the milk but jill’s the vegetative cells of milk-borne pathogens e.g. mycobacterium bovis, salmonella, streptococcus, listeria and brucella
- radiation: two types of radiation: ultraviolet (UV) light and x-rays. The greatest anti microbial activity of UV light occurs at 250-260 nanometers which is the wavelength region of maximum absorption by the poutine and pyramiding bases of DNA
- filtration: preferred method of sterilization of certain solutions e.g. those with heat-sensitive components. The most commonly used filter s composed of nitrocellulose and has a pore size of 0.22 micrometers. Filters work by trapping particles larger than the pore size and retaining somewhat smaller particles by electrostatic attraction of the particles to the filters
