L4 Microbial control.pdf

Microbial Control 7 Stopping reproduction or killing bacteria 1  ÑI Sterilization : It is a process by which an article, surface or medium is made free...

Microbial Control 7 Stopping reproduction or killing bacteria 1  ÑI Sterilization : It is a process by which an article, surface or medium is made free I E of all microorganisms either in vegetative or spore form 1 Disinfection : 64 Destruction of all pathogens or organisms capable of producing infections but not necessarily spores *All organisms may not be killed but the number is reduced to a level that is no longer harmful to health  06H Antiseptics : Chemical disinfectants which can be safely applied to living tissues and are used to prevent infection by inhibiting the growth of microorganisms Ñ Sanitization : Any cleaning technique that mechanically removes microbes  Methods of Controlling Microorganisms Physical methods Chemical methods Sunlight Aldehydes Drying Alcohols Heat Phenols Dry heat Halogens Moist heat Vapor phase Job Filtration Disinfectants i.su Radiation Dyes Salts Surface active agents  Physical methods Sunlight Sunlight has bactericidal activity due to UV rays & heat rays to Sterilizing power varies according to circumstances I said I Natural method of sterilization of water in tanks, rivers and lakes Drying Moisture is essential for the growth of bacteria A Drying in air has a deleterious effect on many bacteria This method is unreliable and is only of theoretical interest  Heat Ñ1 Most reliable method of sterilization Mechanism of action (Dry Heat vs Wet/moist Heat) Dry heat w̅ Kills organisms by protein denaturation, oxidative damage and toxic effects of elevated levels of electrolytes Moist heat I 1 Kills microorganisms by coagulation and denaturation of their enzymes and structural proteins  Dry Heat : Red heat Materials are held in the flame of a Bunsen burner till they become red hot Inoculating wires or loops tw Tips of forceps d Surface of spatula Needles Put it directly on the fire  Dry Heat : Flaming Materials are passed through the flame of a bunsen burner without allowing them to become red hot Glass slides It Scalpels Mouths of culture tubes and bottles Any bacteria or microbes close to the fire will die  Dry Heat : Incineration: sb Materials are reduced to ashes by burning ax Instrument used is incinerator and owl Soiled dressings if Animal carcasses an Bedding Pathological material  Dry Heat : Hot air oven Most widely used method of sterilization by dry heat Used for materials that can withstand high temperatures, but which are likely to be affected by steam We Method of choice for sterilization of glassware, forceps, In scissors, scalpels, swab sticks packed in test tubes Materials such as oils, jellies and powders which are impervious to steam are sterilized by hot air oven Hot air oven Holding temperature and time 1600C for 2 hours 1700C for 1 hour 1800C for 30 minutes Oils, glycerol and dusting powder should be sterilized at 1500C for 1 hour Glass syringes Petri dishes Pipettes Test tubes Scalpels Scissors Forceps Liquid paraffin  able Moist heat: Moist heat is divided into three forms Temperature below 1000C : Pasteurization; water bath At a temperature of 1000C : Boiling; steam; tyndalisation Temperature above 1000C : Autoclave  Pasteurization The process in which a fluid is heated at temperature below boiling point to kill pathogenic vegetative microorganisms (Milk, Beer, Juice) Two methods Holder method (630C for 30 min - rapid cooling to 130C or lower) Flash method (720C for 15-20 secs - Nonsporing pathogens such as rapid cooling to 130C or lower) Mycobacteria; Brucellae; Salmonellae The dairy industry - uses ultra high are destroyed temperature (UHT): 140 to 1500C for 1-3 seconds followed by rapid cooling to 130C or lower)  Temperature at 100°C Boiling at 1000C Boiling at 1000C for 10-30 min kills all vegetative cells Spores need prolonged periods of boiling Uses For the disinfection of medical and surgical equipment – when sterility is not essential in emergency or under field conditions  Is 61 Tyndallisation 6H02 An exposure of steam at 1000C for 20 min on three A Import consecutive days is known as Tyndallization or intermittent sterilization. The instrument used is Koch or Arnold steam sterilizer principle Salmonella First exposure kills all the vegetative forms, and in the I intervals between the heatings the remaining spores germinate into vegetative forms which are killed on subsequent heating Uses Used for sterilization of egg, serum or sugar containing media  Kill bacteriaby steam Temperature above 1000C - Autoclave Holding period/working temperature: 1210C for 15 min (15 psi pressure) f All bacteria will die under this heat and pressure  Autoclave Use autoclave too sterilize Culture media im Rubber material Principle Gowns Dressings Water boils when its vapor pressure Gloves Instruments equals surrounding atmospheric pressure Water containing materials Permeable materials When pressure inside a closed vessel Wet able materials increases, the temperature at which water Disposal cultures of microbial boils also increases Saturated steam has penetrative power and is a better sterilizing agent than dry heat  Filtration Use filtration to sterilize solutions that may be damaged or denatured by high temperatures or chemical agents Bacteria stayup Used for the sterilization of heat labile materials such as Sera Doll Sugar solutions Antibiotics Vitamin solutions  Types of Filters 56 Earthenware filters (Candle filters) Asbestos disc (Seitz) filters Sintered glass filters Membrane filters I Syringe0619 filters Air filters  Earthenware filters Manufactured in several different grades of porosity Ti Used widely for purification of water for industrial and drinking purposes They are of two types dos Unglazed ceramic filters; Ex: Chamberland and Doulton filters dish Compressed diatomaceous earth filters: Ex: Berkefeld and Mandler filters  Asbestos filters Made up of a disc of asbestos (Magnesium trisilicate) Discs are available with different grades of I porosity Sintered glass filters Prepared by fusing finely powdered glass particles Available in different pore sizes Pore size can be controlled by the general particle size of the glass powder  Membrane filters Made of polymeric materials such as cellulose nitrate, cellulose diacetate, polycarbonate and polyester The 0.22 µm and 0.45 µm filter is most commonly used These are routinely used in Water analysis Bacterial counts of water Sterility testing Preparation of solutions  1 SyringeSEP filters Syringes fitted with membrane filters of different pore sizes are available (0.22 and 0.45 µm) For sterilization, the fluid is forced through the disc ima (membrane) by pressing the piston of the syringe  Air filters Air can also be sterilized by filtration Devicename Pass air through high efficiency particulate air (HEPA) filters Used in laminar air flow system in microbiology laboratories HEPA filters can remove particles of 0.3 µm or larger  Radiation Two types of radiations are used for sterilization 1. Non-ionizing 2. Ionising did destroy ÑA Non-ionising radiation if we turniton wemustget outof itsradiationrange These include infrared and ultraviolet (UV) radiations Act by denaturation of bacterial protein and interference with DNA replication (produces thymine dimers) UV radiation is used for disinfecting Bacteriological laboratory Inoculation hoods Laminar flow Operation theatres  Ionizing radiations These include X-rays, Υ (gamma) rays and cosmic rays Has high penetrative power and highly lethal to all cells They damage DNA by various mechanisms Gamma radiations are used for sterilization of disposable items such as Plastic syringes Swabs Culture plates Cannulas Catheters  Since there is no appreciable increase in the temperature, in this method it is known as “cold sterilization” Large commercial plants use gamma radiation emitted from a radioactive element, usually Cobalt 60 The advantage of this method include speed, high penetrating power (it can sterilize materials through outer packages and wrappings)  Chemical methods Aldehydes Dangerousnotoften used Formaldehyde Formaldehyde is active against the aminogroup in protein molecules It is lethal to bacteria and their spores, viruses and fungi It is employed in the liquid and vapor states A 10% aqueous solution is routinely used  Glutaraldehyde Action similar to formaldehyde More active & less toxic than formaldehyde It is used as 2% solution It is available commercially as ‘cidex’ Uses For sterilization of Endoscopes Bronchoscopes Plastic endotracheal tubes Face masks Rubber anaesthetic tubes  Alcohols Ethanol and isopropanol mostly used Used as skin antiseptics Denatures bacterial proteins and rapidly kills No sporicidal or virucidal activity 60-70% alcohol is most effective multe s  Phenols Lethal effect is due to cell membrane damage Phenol (1%) has bactericidal action Kill Phenol derivatives like cresol, chlorhexidine and hexachlorophene are commonly used as antiseptics Cresols (Methylphenols) Lysol is a solution of cresols in soap Most commonly used for sterilization of infected glassware, cleaning floors  Chlorhexidine Savlon (Chlorhexidine and cetrimide) is widely used in wounds, pre-operative disinfection of skin Dettol (chlorhexilenol 4.8% + isopropyl alcohol + pine oil) No action against spores and have very little activity against viruses Has a good fungicidal activity  Halogens Chlorine and iodine are two commonly used disinfectants im on Chlorine is used in the form of bleaching powder, sodium hypochlorite Chlorine is used in water supplies, swimming pools, food and dairy industries Hypochlorites have a bactericidal, fungicidal, virucidal and sporicidal action Bleaching powder or hypochlorite solution are the most widely used Wb  Iodine Iodine in aqueous and alcoholic solution used as skin disinfectant Ñ Iodine applied as tincture of iodine (2% iodine in a water-ethanol solution of Potassium Iodide) Actively bactericidal, moderate action against spores Also active against viruses Compounds of iodine with surface active agents known as iodophores Used in hospitals for preoperative skin degerming Betadine for wounds and Wescodyne for skin  Vapor Phase Disinfectants Sterilizingthewallsceilingetc Formaldehyde gas I Employed for fumigation of heat-sensitive equipment I I 6 (anesthetic 1 machine and baby incubators), operation theatres, wards and laboratories etc. Formaldehyde gas is generated by adding 150 gm of KMnO4 to 280 ml of formalin for 1000 cubic feet of room volume Sterilization is achieved by condensation of gas on exposed surfaces  Ethylene oxide (ETO) Highly lethal to all kinds of microbes including spores Action is due to its alkylating the amino, carboxyl, hydroxyl and sulphydryl groups in protein molecules In addition it reacts with DNA and RNA Highly inflammable and in concentrations (>3%) highly explosive By mixing with inert gases such as CO2, its explosive tendency can be eliminated  Uses ETO gas Used for sterilizing Plastic and rubber articles, Respirators, Heart-lung machines, Sutures, Dental equipment's and clothing It is commercially used to sterilize Disposable plastic syringes, Petri dishes It has a high penetrating power and thus can sterilize prepackaged materials FISTS  Scope of Infection Control Aiming at preventing spread of infection: Standard precautions Transmission based precautions