Sterilization and Disinfection Presented by R.Parthasarathy
TERMS AND DEFINITIONSSterilization The process by which an article, surface or medium is freed of allviable microorganisms either in the vegetative or spore state is known assterilization.Disinfection• The process of destruction of pathogenic microorganisms by directexposure to chemical and physical agents are called as disinfection.• The agents used to achieve these state is called disinfectant.• Chemical disinfectants which can be safely applied to skin or mucousmembrane and are used to prevent infection by inhibiting the growth ofbacteria are called antiseptics.Bactericidal agents and germicides Agents which are able to kill bacteria.Bacteriostatic agents Agents which prevents the multiplication of bacteria ( doesn’t kill).
Various Agents In Sterilization PHYSICAL AGENTS CHEMICAL AGENTS Alcohols: Sunlight Ethanol, isopropyl Aldehydes: Drying Formaldehyde, Glutaraldehyde Dry heat : Dyes Hot air oven, Incineration, Flaming Moist heat:Boiling, Pasteurization, tyndallisation, Auto Halogens claving Filtration Phenolic compounds Gases Radiation Ethylene oxide, Formaldehyde, beta Ionizing, Non Ionizing propiolactone(BPL). Ultrasonic vibration Metallic salts and surface active agents
Physical Agents:Sunlight•Direct sunlight is a natural method of sterilization of water in tanks, rivers andlakes.•Direct sunlight has an active germicidal effect due to the combined effect ofultraviolet and heat rays.Drying•4/5 of the bacterial weight is due to water.•Therefore drying in air has deleterious effect on many bacteria.•This is unreliable method, spores are unaffected by drying.Dry heatFlaming:Inoculating loop or wire, the tip of forceps are held in a Bunsen flame till theybecome red hot.Incineration:This medthod is used to destroy contaminated cloth, animal carcasses andpathological materials.
Physical Agents: cont..Hot air oven This method is applicable to metals, glassware, and some heat-resistant oils and waxes that are immiscible in water.Conditions171ºc for at least one hour.160ºc for at least two hour.121ºc for at least sixteen hour.Moist Heat: Method Uses CommentsWater < 100°c (Pasteurization) For sterilization of serum, vaccines 62°c for 15 min. and body fluids. 72°c for 30 sec. Spores are not destroyed.Water at 100°c For sterilization of glasswares, metal Some spores are not destroyed. and rubber items.Arnold steamer: For sterilization of culture media Preserves properties of media.Stream at atmospheric pressure containing gelatin and sugar.Autoclave : For sterilization of culture media and 121°c at 15 psi for 15-20 minutes.Stream below atm pressure laboratory materials. Almost Kills all the bacteria and spores.Flash autoclaves use 134°C for 3 minutes.
Physical Agents: cont..Filteration:Filtration helps to remove bacteria from large volumes offluid, especially fluid containing heat-labile components such assera, solution of sugars and antibiotics.A pore size of 0.2 m is effective because filters act not onlymechanically but by electrostatic adsorption of particles to theirsurface.The filters are of two types (deep and membrane)
Physical Agents: cont.. FILTERSDEEP FILTERS Made up of Examples Comments and UsesCandle filters 1.Diatomaceous earth Berkefeld filters They are available in different porosity. 2.Unglazed porcelain Chamberlain filters Mostly used for the purification of drinking water and industrial uses.Asbestos filters Asbestos (magnesium Seitz and Sterimat They have high adsorbing capacity and silicate) filters tend to alkalinize the filtered fluid. These are disposable , single use discs available in different grades. Asbestos is carcinogenic hence its use is discouraged.Sintered glass Fusing finely powdered They are expensive and brittle.filters glass particles They have low absorptive property.MEMBRANE Cellulose esters They are routinely used for waterFILTERS Other polymers purification and analysis, sterilization, sterility testing and solutions of parenteral use. Wide range of average pore diameters(APD) are available but 0.2mm size is widely used.
Physical Agents: cont.. RADIATIONNon Ionisizing radiation: Types Produced by Mode of action Uses CommentsLow energy UV lamps DNA damage Infrared rays: Use of UV light(Infrared and Sterilization of prepacked is limited byultraviolet rays) items such as syringes penetration and and catheters. hazardous. Ultraviolet rays: Used for disinfecting operation threatres and laboratories.Ionisizing radiation:High energy Cobalt-60 DNA damage For the sterilization of They areionizing type based antibiotics, hormones expensive.(Gamma rays and instruments and other prepacked They are veryhigh energy disposable items such effective due toelectrons such as as catheters, gloves, high penetrativeX-rays and syringes, infusion sets, power.cosmic rays) oils, animal feeds, etc.
Physical Agents: cont..Ultrasonic and sonic vibration: High frequency sound waves beyond the sensitivity of human ears are called as ultrasonic waves. They have the property to disrupt the cells but the results have been variable. Gram negative rods are more sensitive to ultrasonic vibration whereas Gram positive cocci, spores of fungi and bacteria are resistant to the vibration. Ultrasonic devices are used in dental. However, most sonic machines are not reliable for routine use.
Chemical Agents: cont..Properties of Ideal antiseptics or disinfectants should Effective against all microorganisms and have a wide spectrum of activity. Have speedy action. Be effective in presence of organic matter. Be effective in varying pH(acidic and alkaline medium). Be active in presence of organic matter. Be stable. Also compatible with other antiseptics and disinfectants. Have high penetrating power. Not corrode metals. Not cause local irritation or sensitization. Not interfere with healing. Not be toxic if absorbed into circulation. Be cheap and safe.
Chemical Agents: cont..Factors influencing antiseptics or disinfectants: Time of action. Temperature. Concentration of the substance. pH of the medium. Nature of the organisms. Presence of foreign material.Mode of action Protein coagulation. Disruption of cell membrane. Removal of free sulphydryl groups which is essential for the functioning of the enzymes. Substrate competition.
Chemical Agents: cont..AlcoholsEthyl alcohol, isopropyl alcohol, and n-propanol exhibit rapid, broad-spectrum antimicrobial activity against vegetative bacteria, viruses, andfungi but are not sporicidal.Activity is optimal when they are diluted to a concentration of 60–90% withwater.Protein slows its action whereas 1% mineral acid or alkali enhances theaction.Aldehydes•Formaldehyde is bactericidal, sporicidal, and virucidal.•It is active against the amino group in the protein molecule.•Formaldehyde gas is used for sterilizing instruments and heat sensitive catheters and for fumigating wards, sick rooms and laboratories.•Glutaraldehyde is used for low-temperature disinfection and sterilization of endoscopes and surgical equipment.•It is normally used as a 2% solution to achieve sporicidal activity.
Chemical Agents: cont..DyesTwo groups of dyes are there1.Aniline dyes eg: brilliant green, malachite green, crystal violet2.Acridine dyes eg: proflavine, acriflavine, euflavine and aminacrine.They are used as skin and wound antiseptics.They are more active against Gram positive organisms than Gram negative organisms.HalogensIodine is an effective disinfectant that acts by iodinating or oxidizing essentialcomponents of the microbial cell.Iodine is rapidly bactericidal, fungicidal, tuberculocidal, virucidal, and sporicidal.2% iodine in 50% alcohol (tincture), which kills more rapidly and effectively than alcoholalone.Iodophors (eg, povidone-iodine) are complexes of iodine and a solubilizing agent orcarrier, which acts as a reservoir of the active I2.The most important types of chlorine-releasing agents are sodium hypochlorite,chlorine dioxide, and sodium dichloroisocyanurate, which are oxidizing agents thatdestroy the cellular activity of proteins
Chemical Agents: cont..Phenolic compounds:The use of phenolic compounds are introduced by the Lister.The mode of action is due to their capacity to disrupt the cell membrane.Phenol(carbolic acid) is a potent protein denaturant and bactericidal agent.It is used as disinfectants for various hospital purposes.Cresol and Lysol are active against a wide range of organisms but they aretoxic and corrosive.They are used to disinfect surgical instruments, contaminated materials andfloors.Halogenated diphenyl compounds such as hexachlorophene andchlorhexidine.Hexachlorophene is toxic and should be handled with care.Cholrhexidene is nontoxic, hence used as skin antiseptic which is moreeffective against Gram positive organisms than Gram negative organisms.
Chemical Agents: cont..Gases:Ethylene oxide is an inflammable and potentially explosive gas.By mixing with inert gases like CO2 and N2 to concentration of 10% itsexplosive tendency is eliminated.It is an alkylating agent that inactivates microorganisms by replacing labilehydrogen atoms on hydroxyl, carboxy, or sulfhydryl groups, particularly ofguanine and adenine in DNA.Under controlled condition it is used to sterilise materials such as glass,artificial heart valves, respirators, lung machines, equipments and clothing.Formaldehyde gas and Betapropiolactone(BPL) are used for fumigation ofoperation theatres and other rooms.BPL is more efficient than formaldehyde gas.
Chemical Agents: cont..Surface active agentsThese compounds have two regions in their molecular structures, one awater-repelling (hydrophobic) group and the other a water-attracting(hydrophilic) group.They are classified into four groups; anionic, cationic, nonionic andamphoteric.They are mainly used as wetting agents, emulsifiers and detergents.Cationic detergents, particularly the quaternary ammonium compounds(“QACs") such as benzalkonium chloride, acetyl trimethyl ammoniumbromide are highly bactericidal.They are effective against Gram +ve organisms than Gram –ve organisms.They are more active in alkaline pH.They are inactive against spores and viruses, tubercle bacilli.Anionnic detergents Eg; common soap.Amphoteric or ampholytic compounds or tego compounds are active againstGram+ve organisms than Gram –ve organisms.Generally it is not used.
Chemical Agents: cont..Metallic saltsSalts of mercury, copper and silver are used as disinfectant.Mercuric chloride is highly toxic. Hence organic compounds such asmercurochrome, phenyl mercury nitrate and thiomersal are used asantiseptics(less toxic).Copper salts are used as fungicides.Silver salts in aqueous solution have a limited use.Testing of DisinfectantsBecause of numerous parameters which influence disinfectant activity, thereis no reliable test to determine the efficiency of a disinfectant.However Phenol is used as standard.