Lab 2 Sterilization and Disinfections PDF

Practical Microbiology I Lab. 2 Sterilization and Disinfections Pharmacist : Muthanna Taha  Sterilization and Disinfections Sterilization: a process of complete elimination or destruction (killing) of all forms of microbial life (i.e., both vegetative and spore forms), wh...

Practical Microbiology I Lab. 2 Sterilization and Disinfections Pharmacist : Muthanna Taha  Sterilization and Disinfections Sterilization: a process of complete elimination or destruction (killing) of all forms of microbial life (i.e., both vegetative and spore forms), which is carried out by various physical and chemical methods. Disinfection: is the process of reducing or eliminating harmful microorganisms from inanimate (a non-living) objects and surfaces.  Methods of Disinfection and Sterilization Physical methods A. Heat: 1- Dry 2- moist B. Radiation: 1- U.V. Light 2- Ionizing radiation C. Filtration Chemical methods 1. Alcohols : both ethanol and isopropanol are widely used, normally at a concentration of about 70%. (water is needed for protein denaturation). They are bactericidal and fungicidal. 2. Aldehydes 3. Formaldehyde 4. Halogens 5. Phenols  Physical Methods A. Heat 1. Dry heat a) Direct flaming : simplest method is exposing the item to be sterilized to the naked flame e.g. Bunsen burner for sterilizing bacteriological loops, Knives, blades.  Physical Methods b) Hot air oven: expose items to 160-180⁰C for (0.5-1) hour and this used for metals, glassware, oils, waxes, powders. c) Incineration : this is an excellent method of destroying materials such as contaminated cloth, animal carcasses and pathological materials.  Physical Methods 2. Moist heat (Like boiled water and used to kills microorganisms by denaturing proteins) 1. Boiling : (very common). 2. Tyndallization : The process involves exposure of material to hot steam (100⁰C) for a period (20 minutes) at atmospheric pressure, then cooling and incubating for a day, this is repeated for 3 successive days. The three incubation periods are to allow heat-resistant spores (that surviving before the boiling period) to germinate to form the heat- sensitive vegetative(growing) stage, which can be killed by the next boiling step.  Physical Methods 3. Pasteurization: involves heating liquids at high temperatures for short time followed by cooling, it kills harmful microbes in milk without affecting the taste or nutritional value. (72⁰C for 15-30 mins). 4. Autoclave: The autoclave works on the principle that the high pressure inside the chamber increases the boiling point of water for the sterilization of equipment, while ensuring the rapid penetration of heat into the deeper parts of equipment. (121⁰C at 15-20 mins).  Tyndallization Autoclave  Physical Methods B. Radiation 1- Ultra violet (UV) light radiation: Light has limited sterilizing power because of poor penetration into most materials. Generally used in irradiation of air in certain areas e.g. operating rooms. 2- Ionizing radiation: One of them gamma radiation produced by cobalt 60, it has greater energy than U.V. light, therefore more effective. Used mainly in industrial facilities for sterilization of disposable plastic syringes, gloves, specimens containers and petri dishes.  UV light Gamma radiation  Physical Methods C. Filtration Best known example is the membrane filter made from cellulose acetate (Millipore). Generally remove most bacteria but viruses and small bacteria e.g. Chlamydia and Mycoplasma may pass through it. Thus filtration does not technically sterilize items but it is adequate for circumstances under which it is used. Mainly used for heat labile substances e.g. in serology (Ag-Ab), antibiotics.