STERILIZATION AND DISINFECTION - The Lung Center

STERILIZATION ANDDISINFECTION

Importance of hand washing shown by Semmelweis

STERILIZATION• A physical or chemical process that destroysor eliminates all forms of microbial life,including spores.• A satisfactory sterilizing process may beregarded as one that achieves a highprobability of sterility i.e. a process that killsmore than 10 6 organisms ,including spores ofdefined exceptionally high degree ofresistance.

METHODS OFSTERILIZATION• Determined by the character of items to besterilized.• Choice of process requires knowledge ofthe equipment and of stability of thematerial to be sterilized.

CLASSIFICATIONPHYSICAL1) DRY HEAT2) STEAM STERILIZATION3) INCINERATION4) FILTERATION5) RADIATION1) ETHYLENE OXIDECHEMICAL2) GLUTARALDEHYDE

PHYSICAL METHODSDRY HEAT STERILIZATION• For heat stable materials• Sterilization effect is due to enzymeinactivation, protein denaturation or both.

• Red heat: Inoculating wires and loops, pointsof forceps ,surface of searing spatulas.• Hot air sterilizers: Glassware, glasssyringes, glass pipettes.• British standards(BS3421)• Should be fitted with a fan that providesforced air circulation throughout the ovenchamber, a temperature indicator, a controlthermostat and timer, open mesh shelving

STEAM STERILIZATION• AUTOCLAVE: Provides moist heat attemperatures above 100°C by exposingthe load to saturated steam at pressuresgreater than atmospheric.• As steam condenses on the cooler load, itreleases both thermal energy andmoisture ,which together denature allmicrobial proteins.

AUTOCLAVE

TIME AND TEMPERATURE REQUIREDFOR STERILIZATION IN THEAUTOCLAVESterilizingtemp (°C)Pressure aboveatmospheric(bar)Sterilizationhold time(min)121-124 1.1 15134-138 2.2 3

TYPES OF AUTOCLAVES1) Simple laboratory autoclave2) Transportable bench top autoclaves3) Large simple autoclaves4) Downward displacement autoclaves5) Multipurpose laboratory autoclaves.

STERILIZATION BY1) Membrane filtersFILTERATION2) Syringe filters3) Vaccum & “in line” filters4) Pressure filtration5) Air filters- HEPA

STERILIZATION BYRADIATION• IONIZING radiation - γ radiation fromradioactive elements ,usually Co 60• ULTRAVIOLET RAYS: Mercury vapourlamps emitting radiation in the range of250-260nm are bactericidal & to a lesserextent sporicidal.

CHEMICAL METHODS1)ETHYLENE OXIDE: Medical & surgicalarticles.Highly lethal gas.Attaches to sulphydryl bonds &proteinsthereby interfering with their structure andfunction.Effect most rapid at 30-40% relativehumidity.DISADVANTAGES:Toxic and highlyexplosive.

CHEMICAL METHODS(CONTD.)2) Glutaraldehyde:• Chemically related to formaldehyde but is2-8 times more sporicidal.• In a 2% alkaline aqueous solution it issporicidal at room temperature• Used to sterilize plastics, rubber &delicatelensed instruments

DISADVANTAGES• Significant loss of activity in the alkalinestate (over a 2 week period).• Exposure of at least 10 hours required.• Need to remove residual glutaraldehydeby rinsing with sterile water.

3) Gas plasma:A very small quantity of hydrogen peroxide invarious phases, including a low temperaturegas plasma exited by radio waves .Sporicidal,bactericidal ,virucidal.

BIOLOGICAL CONTROLS OFDIFFERENT STERILIZATIONMETHOD OFSTERILIZATIONHot air ovenAutoclaveEthylene oxideIonizingradiationsFilterationMETHODSBIOLOGICAL CONTROLBacillus subtilis subsp.nigerBacillus stearothermophilusBacillus globigiBacillus pumilisSerratiamarcescens,Pseudomonas

CHEMICAL CONTROL• A Browne’s tube containing a red solutionis placed within the load. A change ofcolour of the solution to green indicatesproper sterilization.

DISINFECTION• It is a process whereby pathogenicorganisms, but not necessarily allmicroorganisms or spores are destroyed.Disinfectants are used in hospitals andclinical laboratories for three main purposes :1)To render contaminated objects safe forfurther use.2)To reduce the microbial contamination of theinanimate environment.3)To prevent spread of microorganisms bycontaminated wastes.

COMMON DISINFECTION• PHYSICALPROCEDURES1)Hot water or steama) At temperature below 100°C -Pasteurisationb) At temperature of 100°C –Boiling/Freesteam/Tyndallizationc) At temperature above 100°C -Autoclaving2)Ultraviolet rays

CHEMICAL1)Phenols & cresols2)Halogens3)Metallic salts4)Aldehydes5)Alcohols6)Dyes7)Vapour phase disinfectants.8)Surface active disinfectants.

COMMON DISINFECTANTS ANDTHEIR CONCENTRATIONSDISINFECTANT CONCENTRATIONEthanol 70%Methylated spirit 70%Glutaraldehyde 2%activated(Cidex)Bleaching powder 14g/l of waterSod.hypochlorite 1%,0.1% solutionH 2 O 3%solution2Lysol 2.5% solutionSavlon 2.0%,5%

TESTING OF DISINFECTANTS1)Minimum inhibitory concentration (MIC)2)Phenol coefficient-Rideal Walker-Chick Martin3)Capacity test (Kelsey & Skyes test)

ANTISEPSIS• It is the use of a substance that preventsor arrests the growth or action ofmicroorganisms either by inhibiting theiractivity or by destroying them.• The term “antiseptic” is used especially forpreparations applied to living tissue.

AREAS OF USE• AIM OF ANTISEPSIS- Reduction ordestruction of undesirable microorganismson skin & mucosal surfaces whilepreserving the normal, resident flora.

REQUIREMENTS ONANTISEPSIS &ANTISEPTICS1) Lack of skin/mucosal irritancy2) Lack of systemic toxicity (usually measuredas oral toxicity)3) Lack of teratogenic,mutagenic&carcinogenic effects)4) Absorbed blood levels in man must be farbelow the toxic levels for both long &shortterm exposure.5) Stability in both concentrated &use –dilutionforms.

COMMONLY USEDANTISEPTICS1)Heavy metals: Mercurials,silver nitrate,silversulfadiazine2)Bisphenols: Hexachlorophene3)Alcohols:Ethanol at concentration of 70-90%4)Iodine & iodophors5)Quaternary ammonium compounds7)Phenols

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