State University of New York at BuffaloSchool of Medicine and Biomedical SciencesDepartment of Microbiology and ImmunologyMicrobiology 301D. DombroskiFebruary 3, 2012 829-2355Sterilization and DisinfectionControl of Infectious Disease Agents1. public sanitation2. sterilization and disinfection procedures3. chemotherapeutic agents4. bodies defense mechanismsTerminologySterilization- total destruction of all microbesDisinfection – the destruction and removal of most pathogenic microbes from inanimate objects. All microbes are not removed – remaining are nonpathogens and spores of pathogens. A disinfectant is the chemical agent used. Bacteriocidal – an agent that kills bacteriaBacteriostatic – an agent that inhibits bacterial growthAntiseptic – chemicals with low human toxicity that destroy microorganisms capable of causing contamination or diseaseFactors Affecting Sterilization/Disinfection Action1. time2. temperature3. pH14. number of microorganisms5. types of microorganisms6. presence of extraneous matter7. proper exposure8. concentration of disinfectant or sterilantMethods of Physical ControlI. Heat – high temperatures inactivate proteins and nucleic acids by breaking their hydrogen bondsII. Radiation – causes chemical changes to the nitrogenous bases of nucleic acidsIII. Filtration – physical removal of organisms from the solution that is filteredI. Heat- most widely used method for microbial control- heat sterilization parameters – temperature, duration and humidity- decimal reduction time or D value – measures on organism’s heat resistanceSterility Tests1. Heat sensitive tape – tape impregnated with chemicals that change color when exposed to a critical temperature2. Biological monitor – spore strips of Clostridium or Bacillus2Heat Treatment ProceduresA. dry heatB. moist heatC. boiling waterD. pasteurization flash pasteurizationDry heat – generated by an ovencondition - 160C, two hour – kills sporesusage – sterilization of laboratory glasswaredisadvantage – high temperature, chars organic materialsMoist Heat – generated by an autoclave (industrial pressure cooker)condition - 121C, 15 minutes, 15 lb/in2 – kills sporesusage – sterilization of microbiological media, glassware and commercial canningdisadvantage – expensive equipmentBoiling water – water bath or chambercondition - 100C for 30 minutes – kills all non-spore forming microorganismsusage – hospitals – disinfect bedding/clothing of patients home – boil unsafe drinking water, disinfect baby items (food preparation and utensils)disadvantage – items easily recontaminated when removed from waterPasteurization - process of using mild heat to kill pathogens while preserving the quality and flavor of food3condition - 62 to 66C, 30 minutes, quick cool Time and temperature conditions required to kill Coxiella burnettiusage – destruction of pathogens in milk, beer and wine – increases shelf lifeFlash Pasteurization – newer technique condition – 71.7C, 15 seconds, quick coolII. RadiationThe emission and propagation of energy through space or through a substance in the form of wavesA. Ultraviolet (UV) light (non-ionizing)B. Ionizing radiationA. Ultraviolet light – 100 – 400 nm wavelengthBacteriocidal wavelength – (250-270 nm) DNA absorbs UV light which induces arearrangement in hydrogen bonding of the DNA strand. These changes result in copying errors which increase the probability of a lethal mutationGermicidal lamp (mercury vapor lamp) – generates radiation at 254 nmusage – disinfection rather than sterilization lamps are placed in air ducts or directly over surface. UV lamps are placed in air supply ducts of operating rooms, food preparation areas, nursing homes and nurserieseffectiveness – reduces the concentration of air-borne microbes by 99%.disadvantage – limited use since UV light is absorbed by solids – damaging to 4human tissues (skin and eye) – sunburn, wrinkles, cancer and retinal damageB. Ionizing Radiation – shorter wavelength than UV – shorter wavelength: increased energy, energy is absorbed by atoms ions (gain/loss of electrons) Ionization forms primarily free hydroxyl radicals which react with cellular proteins and nucleic acids, inducing chemical alterations that are cidal. usage – 1. sterilizing medical products – drugs, vaccines, medical instruments (especially plastics), syringes, sutures, catheters, surgical gloves and tissues such as bone, skin and heart valves 2. sterilization of meat, fruits and some vegetables advantage – 1. speed 2. high penetration power – ability to penetrate fabrics, plastics, liquids and foods for sterilizationdisadvantage – radiation exposureIV. FiltrationSterilization technique for removing microbes, not destroying them. Fluid (air or liquid) is strained through a layer of material with openings (pore sizes) large enough for the fluid to pass through but too small for microorganisms. Filter membranes – cellulose acetate, polycarbonate, variety of plastics (Teflon or nylon)0.22 m pore size – removes all bacteria50.025 m pore size – removes all virusesLiquid filtration - used to sterilize liquids that cannot withstand heat – (serum, blood products, vaccines, antibiotics, IV fluids and enzymes)Water purificationAir filtration – HEPA (high efficiency particulate air filters) are used in air ducts to critically clean areasHEPA filter – tightly woven fiberglass medium which remove particles as small as 0.3m with 99.9% efficiencyUsage – HEPA filters are installed in air supply systems to operating rooms, nurseries, intensive care units and biohazard hoods. Methods of Chemical ControlA. Alcohols – ethyl alcohol, isopropyl alcoholB. Halogens – iodine, chlorineC. Aldehydes – formaldehyde and glutaraldehydeD. Heavy metals – copper, mercury, silverE. Gases – ethylene oxideF. Surface active agents (cationic detergents) – quaternary ammonium compoundsG. Phenols – natural (carbolic acid) – ammonium compounds derivatives (o-phenylphenol and hexachlorophene)H. Oxidizing agents – hydrogen peroxideA. Alcohols6Ethyl alcohol and Isopropyl alcohol are