Sterilization and DisinfectionSterilization and Disinfection
SterilizationSterilization is the killing or removal ofis the killing or removal ofall microorganisms, including bacterialall microorganisms, including bacterialspores. It is an absolute germ free state.spores. It is an absolute germ free state. DisinfectionDisinfection is the killing of many butis the killing of many butnot all, microorganisms. Speciallynot all, microorganisms. Speciallybacterial spores are not killed.bacterial spores are not killed. DisinfectantDisinfectant is a chemical agent that isis a chemical agent that isused for disinfection.used for disinfection.
Methods of sterilization:Methods of sterilization:I. HeatI. HeatII. Ionizing radiationsII. Ionizing radiationsIII. FiltrationIII. FiltrationIV. ChemicalsIV. ChemicalsI.I. HeatHeat::It can be againIt can be againa. Dry heata. Dry heatb. Moist heatb. Moist heatc. Pasteurizationc. Pasteurization
a.a. Dry HeatDry Heat:: Sterilization by dry heat requiresSterilization by dry heat requirestemperatures in the range of 180°C for 2temperatures in the range of 180°C for 2hours.hours. Used primarily for glassware.Used primarily for glassware. Used less frequently than autoclaving.Used less frequently than autoclaving. Dry heat can be applied byDry heat can be applied byi.i. Red heat:Red heat:The article to be sterilized is directly held inThe article to be sterilized is directly held inthe flame and heated till it becomes red hot.the flame and heated till it becomes red hot.ii.ii. Hot air oven:Hot air oven: Articles are sterilized in hot air oven at tempArticles are sterilized in hot air oven at temprange of 160range of 16000C-180C-18000C.C.
16016000C is sterilization temperature.C is sterilization temperature. Uses: Glassware, sealed containers. etcUses: Glassware, sealed containers. etcare sterilized by this method.are sterilized by this method.
b.b. Moist heatMoist heat:: It can be applied byIt can be applied by1.1. BoilingBoiling2.2. SteamingSteaming1.1. BoilingBoiling:: Simple boiling is used to sterilize someSimple boiling is used to sterilize someglassware.glassware.
Boiling done for 20-30 minutes forBoiling done for 20-30 minutes forthree consecutive days is calledthree consecutive days is calledTyndalization. It is used for materialsTyndalization. It is used for materialswhich can not withstand prolongedwhich can not withstand prolongedboiling.boiling.2.2. SteamingSteaming Most common method to be used. It isMost common method to be used. It isnormally applied above 100normally applied above 10000C underC underhigh pressures. The instrument usedhigh pressures. The instrument used
Principle of autoclavingPrinciple of autoclaving:: In autoclave steam or moist heat isIn autoclave steam or moist heat isproduced at a temp of 115produced at a temp of 11500C.C. Water boils at 100Water boils at 10000C. At this temp vapourC. At this temp vapourpressure equals the atmospheric pressurepressure equals the atmospheric pressurei.e. 760 mm Hg. When water is heated ini.e. 760 mm Hg. When water is heated ina closed vessel the vapour pressure risesa closed vessel the vapour pressure riseswith a subsequent rise in boiling point.with a subsequent rise in boiling point.The boiling point rises to 115The boiling point rises to 11500C.C.
Thus steam produced at this temp isThus steam produced at this temp issuper heated.super heated. This steam when condenses on theThis steam when condenses on thearticles thermal energy is released fromarticles thermal energy is released fromit and along with moisture this heatit and along with moisture this heatdenatures the microbial proteins.denatures the microbial proteins. Autoclave is used to sterilize most of theAutoclave is used to sterilize most of theinstruments and culture media.instruments and culture media.
Different temperatures for autoclave atDifferent temperatures for autoclave atdifferent pressures.different pressures. 11511500C at 10 psiC at 10 psi 12112100C at 15 psiC at 15 psi 13213200C at 27 psiC at 27 psi
c.c. PasteurizationPasteurization:: It is used primarily for milk.It is used primarily for milk. It consists of heating the milk to 62°CIt consists of heating the milk to 62°Cfor 30 minutes followed by rapid coolingfor 30 minutes followed by rapid cooling OR heating it at 72OR heating it at 7200C for 20 seconds.C for 20 seconds. This is sufficient to kill the vegetativeThis is sufficient to kill the vegetativeforms of the milk-borne pathogens, e.g.forms of the milk-borne pathogens, e.g.Mycobacterium bovis, Salmonella,Mycobacterium bovis, Salmonella,Streptococcus etcStreptococcus etc
II.II. Ionizing radiationsIonizing radiations:: The three types of radiation used to killThe three types of radiation used to killmicroorganismsmicroorganisms 1.Ultraviolet (UV) light and 2. X-rays. 3.1.Ultraviolet (UV) light and 2. X-rays. 3.Gamma raysGamma rays Used in industry to sterilize disposableUsed in industry to sterilize disposablesyringes, gloves, catheters etc.syringes, gloves, catheters etc.III.III. FiltrationFiltration:: Filtration is the preferred method of sterilizingFiltration is the preferred method of sterilizingcertain solutions, e.g. IV fluids. Antibioticcertain solutions, e.g. IV fluids. Antibioticsolutions.solutions. Cellulose acetate membrane filter mostCellulose acetate membrane filter mostcommon.common. Pore size 0.02-1 µm. Removes bacteria.Pore size 0.02-1 µm. Removes bacteria.
High-efficiency particulate air (HEPA)High-efficiency particulate air (HEPA)filters remove almost all microorganismsfilters remove almost all microorganismslarger than about 0.3 micron in diameter.larger than about 0.3 micron in diameter. They are used to remove microThey are used to remove microorganisms from air. Used specially in TBorganisms from air. Used specially in TBlabs.labs.
Filter sterilization with a disposable, presterilizedFilter sterilization with a disposable, presterilizedplastic unit.plastic unit.
IV.IV. ChemicalsChemicals: They can be: They can bea. Gases like Ethylene dioxide used ina. Gases like Ethylene dioxide used inplastic industry. Highly toxicplastic industry. Highly toxicinflammable ,potentially explosiveinflammable ,potentially explosivegas .gas .b. Liquids like Glutraldehyde used tob. Liquids like Glutraldehyde used todisinfect endoscopes.disinfect endoscopes.
Methods of DisinfectionMethods of Disinfection:: DisinfectantsDisinfectants are strong chemicals usedare strong chemicals usedfor disinfecting non living articles.for disinfecting non living articles. They are toxic and corrosives for livingThey are toxic and corrosives for livingtissues.tissues. AntisepticsAntiseptics:: Disinfectants which are less irritant andDisinfectants which are less irritant andcan be applied to living tissues are calledcan be applied to living tissues are calledantiseptics e.g. methylated spirit,antiseptics e.g. methylated spirit,Alcohol, Iodine, Chloroxylenol (dettol)Alcohol, Iodine, Chloroxylenol (dettol)
Types of Disinfectants.Types of Disinfectants.1.1.Phenol and Phenolic compoundsPhenol and Phenolic compounds.. Phenol (carbolic acid) and phenolics arePhenol (carbolic acid) and phenolics aregood disinfectants.good disinfectants. Phenolics are derivatives of Phenol.Phenolics are derivatives of Phenol. Cresols is derived from coal tar form anCresols is derived from coal tar form animportant group of phenolics.important group of phenolics.2.2.BisphenolsBisphenols:: Bisphenols are derivatives of phenol.
Hexachlorophene and Triclosan areHexachlorophene and Triclosan areimportant bisphenols.important bisphenols.3.3. Biguanides: The best known biguanide ischlorhexidine used for microbial controlon skin and mucous membranes. Hibiscrub (chlorhexidine + cetrimide )Hibiscrub (chlorhexidine + cetrimide )Hibisol (chlorhexidine + glycerine)Hibisol (chlorhexidine + glycerine)
4.4. Halogen compoundsHalogen compounds.. The halogens, particularly iodine andThe halogens, particularly iodine andchlorine, are effective antimicrobialchlorine, are effective antimicrobialagents.agents. TheThe most common commercialmost common commercialpreparation of Iodine is povidone-iodinepreparation of Iodine is povidone-iodine(Pyodine).(Pyodine). A liquid form of compressed chlorine gasA liquid form of compressed chlorine gasused extensively for disinfectingused extensively for disinfectingmunicipal drinking water, water inmunicipal drinking water, water inswimming pools, and sewage.swimming pools, and sewage.
3.3. Aldehydes:Aldehydes: Formaldehyde as gas used to sterilizeFormaldehyde as gas used to sterilizeoperation theatres and other spaces.operation theatres and other spaces. Glutaraldehyde a chemical relative ofGlutaraldehyde a chemical relative offormaldehyde less irritating and moreformaldehyde less irritating and moreeffective than formaldehyde.effective than formaldehyde. Glutaraldehyde used to disinfect hospitalGlutaraldehyde used to disinfect hospitalinstruments, including endoscopes andinstruments, including endoscopes andrespiratory therapy equipmentrespiratory therapy equipment
4.4. AlcoholAlcohol:: Alcohols effectively kill bacteria andAlcohols effectively kill bacteria andfungi but not spores and non envelopedfungi but not spores and non envelopedviruses.viruses. Most commonly used alcohols areMost commonly used alcohols areethanol and Isopropanol.ethanol and Isopropanol. The recommended conc. of ethanol isThe recommended conc. of ethanol is70%70% Isopropanol is slightly superior toIsopropanol is slightly superior toethanol as an antiseptic and disinfectantethanol as an antiseptic and disinfectant However, alcohols are unsatisfactoryHowever, alcohols are unsatisfactoryantiseptics when applied to wounds.antiseptics when applied to wounds.