DISINFECTION and STERILIZATION PDF

1 STERILIZATION AND DISINFECTION DISINFECTION and STERILIZATION Faculty of Medicine University of Zintan  2...

1 STERILIZATION AND DISINFECTION DISINFECTION and STERILIZATION Faculty of Medicine University of Zintan  2 STERILIZATION AND DISINFECTION Disinfectants and antiseptics differ from systemically active antimicrobials in that they possess little selective toxicity. They are toxic not only for microbial pathogens but for host cells as well. Therefore, they can be used only to inactivate microorganisms in the inanimate environment or, to a limited extent, on skin surfaces. They cannot be administered systemically.  3 STERILIZATION AND DISINFECTION Definitions Sterilization- A process by which an article, surface or medium is freed of all microorganisms (pathogenic/ nonpathogenic) either in their vegetative or spore state. - Can be carried out by physical or chemical methods. - Physical methods- moist heat, dry heat. - Chemical methods- ETO gas, Hydrogen peroxide. Results in reduction of ≥106 log CFU of microorganisms & their spores.  4 Antiseptics STERILIZATION AND DISINFECTION (Greek αντι, against, and σηπτικος, putrefactive) are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction. They should generally be distinguished from antibiotics that destroy microorganisms within the body, and from disinfectants, which destroy microorganisms found on non-living objects. Some antiseptics are true germicides, capable of destroying microbes (bacteriocidal), whilst others are bacteriostatic and only prevent or inhibit their growth. Antibacterials are antiseptics that only act against bacteria.  5 STERILIZATION AND DISINFECTION Some common antiseptics Alcohols Quaternary ammonium compounds Boric acid Chlorhexidine Gluconate Hydrogen peroxide Iodine Mercurochrome Octenidine dihydrochloride Phenol (carbolic acid) compounds Sodium chloride Sodium hypochlorite  6 STERILIZATION AND DISINFECTION Disinfectants are antimicrobial agents that are applied to non-living objects to destroy microorganisms, the process of which is known as disinfection. Disinfectants should generally be distinguished from antibiotics that destroy microorganisms within the body, and from antiseptics, which destroy microorganisms on living tissue. Sanitisers are high level disinfectants that kill over 99.9% of a target microorganism in applicable situations. Very few disinfectants and sanitisers can sterilise (the complete elimination of all microorganisms), and those that can depend entirely on their mode of application. Bacterial endospores are most resistant to disinfectants, however some viruses and bacteria also possess some tolerance.  7 STERILIZATION AND DISINFECTION Types of disinfectants Alcohols Aldehydes Halogens Oxidising agents Quaternary ammonium compounds Other  8 STERILIZATION AND DISINFECTION Disinfection- destruction/ removal of all disease causing organisms except spores. Results in reduction of at least ≥103 log CFU of most microorganisms High level disinfectant Intermediate level Low-level disinfectants (HLD) disinfectant (ILD) (LLD) Capable of killing all Destroy all Destroy vegetative microorganisms & microorganisms, but bacteria & enveloped bacterial spores when not bacterial spores viruses; variable action used in sufficient on nonenveloped viruses concentration under & fungi, but no action on suitable conditions tubercle bacilli & spores Antiseptics- disinfectants which can safely be used on living tissues (used for asepsis)  9 STERILIZATION AND DISINFECTION Sanitization- disinfection used in connection with food & catering equipment. Decontamination/cleaning- process by which an area or article is rendered free of contamination (microbial, chemical or radioactive) to a level at which items are considered as safe without protective attire. Results in reduction of at least ≥1 log CFU of most of microorganisms but not spores.  10 STERILIZATION AND Level of Spores Tubercle Non Fungi Vegetative DISINFECTION Enveloped disinfectant bacilli enveloped bacteria viruses viruses 1. Sterilant YES YES YES YES YES YES 2. Disinfectant a) HLD +/- YES YES YES YES YES b) ILD NO YES YES YES YES YES c) LLD NO NO +/- +/- YES YES  11 STERILIZATION AND 1. PHYSICAL AGENTS DISINFECTION i. Sunlight ii. Drying iii. Dry heat a. Flaming b. Incineration c. Hot air oven iv. Moist heat 1. Temperature below 100 C a. Pasteurization b. Inspissation c. Vaccine bath/water bath 2. Temperature at 100 C a. Boiling b. Koch’s/Arnold’s steam sterilizer c. Tyndallization  12 STERILIZATION AND DISINFECTION 3. Temperature above 100 C a. Autoclave v. Filtration a) Depth filters. b) Membrane filters. vi. Radiation a) Ionizing radiation: γ rays, X ray, cosmic ray. b) Non ionizing radiation: UV, Infra red. vii. Ultrasonic & sonic vibration  13 STERILIZATION AND DISINFECTION 2. Chemical agents i. Alcohols a. Ethyl alcohol b. Isopropyl alcohol ii. Aldehydes a. Formaldehyde b. Glutaraldehyde c. Orthophthaldehyde iii. Dyes- aniline, acridine dyes. iv. Halogens- chlorine, iodine & iodophores. v. Phenolics- cresol, lysol, chloroxylenol. vi. Biguanides- chlorhexidine gluconate.  14 STERILIZATION AND DISINFECTION vi. Surface active agents: Quarternary ammonium compounds. vii. Metallic salts: Mercuric chloride, copper salts. viii. Gases a) Ethylene oxide. b) Formaldehyde. c) Beta propiolactone. ix. Gas plasma sterilants a) Low temperature steam formaldehyde. b) Ethylene oxide(ETO). c) Beta propiolactone. d) Plasma sterilization  15 STERILIZATION AND DISINFECTION Physical agents  16 STERILIZATION AND DISINFECTION 1. Sunlight Ultraviolet rays of sunlight has bactericidal activity leading to spontaneous natural sterilization. Ultraviolet rays are filtered by ozone layer & impurities in atmosphere but in tropical countries where there is less impurity there is appreciable bactericidal effect. 2. Drying Water constitutes 80% of body weight of bacteria therefore drying has deleterious effect on bacterial growth but bacterial spores are unaffected.  17 STERILIZATION AND DISINFECTION 3. Heat Most reliable method of sterilization, method of choice unless contraindicated.  Dry heat: kills by protein denaturation, oxidative damage, toxic effect of elevated electrolytes.  Moist heat: kills by protein denaturation & coagulation.  18 STERILIZATION AND Dry heat methods DISINFECTION 1. Red heat: process of sterilization in which inoculating loops & wires, tips of forceps & scissors are held vertically in flame until red hot. 2. Flaming: Scalpel blades, glass slides, mouth of culture tubes, bottles are exposed to flame for few sec w/o heating them to become red hot. 3. Incineration: efficient method of sterilization for destroying contaminated materials such as soiled dressings, animal carcasses & pathological materials. Disadvantage Polystyrene materials cannot be incinerated because they emit clouds of dense toxic smoke but plastics like poly vinyl chloride & polythene can be incinerated.  19 STERILIZATION AND 4. Hot air oven DISINFECTION Most widely used method of dry heat sterilization for sterilizing loads that might be damaged by moist heat but can tolerate high temperature (160 C- 180 C). Acts by oxidation of cell constituents. Used to sterilize 1. Glass wares (petri dishes, pipettes, tubes, measuring cylinders, flasks, glass syringes). 2. Forceps & scissors. 3. Scalpels. 4. Swab sticks & some pharmaceutical products like liquid paraffin, dusting powder, fats. Operated electrically with heating elements in walls of chamber.  20 STERILIZATION AND DISINFECTION A fan is fitted inside for even distribution of air. A temperature indicator, a control thermostat and timer, open mesh shelving and adequate wall insulation. Sterilization temp is set to ensure that sterilization hold time starts only when required temp is reached as detected by the thermocouples.  21 STERILIZATION AND DISINFECTION Method of operating hot air oven Materials to be sterilized are cleaned, dried & packed loosely to allow free circulation of air & optimum heat transfer. Glass test tubes with slip on aluminium caps are placed vertically in metal racks. Ends of pipettes stoppered to a depth of 2 cm with non-absorbent cotton wool & kept in metal canisters. Powders, fats, oils, greases are sterilized in sealed metal containers.  22 STERILIZATION AND Temperature- time cycle DISINFECTION Temperature (C) Holding time (mins) 160 120 170 60 150 150 Oven is cooled for 2 hrs before door is opened.  Sterilization controls:- 1. Spores of Bacillus atrophaeus are used as sterilization control. 2. Spores of nontoxigenic strains of Clostridium tetani are used to test efficacy of dry heat sterilization. 3. Browne’s tube: Containing red colour solution which turns green on proper sterilization.  23 STERILIZATION AND Moist heat DISINFECTION I. Temp below 1000 C 1. Pasteurization Method used for control of microorganisms in beverages like fruits/ vegetables juices, and milk. - Holder method- Heated at 630C for 30 min. - Flash method- heated at 720C for 20 sec followed by rapid cooling to 13°C. - UHT Sterilisation- milk & milk products are heated at 140-150°C for 1-3 sec.  24 STERILIZATION AND DISINFECTION 2. Water bath- vaccines or serum containing coagulable protein are kept in a water bath at 600C for 1 hour. eg. Typhoid vaccine. 3. Inspissation (fractional sterilization)- media like Lowenstein Jensen’s medium can be heated at 80-850C for 30 min on 3 successive days by a special instrument called Inspissator.  25 STERILIZATION AND DISINFECTION II. Temp at 1000C 1. Boiling: vegetative bacteria die almost immediately but spores require a longer time, about 20- 30 mins are required to kill; not ideal for surgical instruments. 2. Steam at atmospheric pressure: (Koch’s/ Arnold steam sterilization)- A single exposure of 90 mins usually ensures sterilization. 3. Tyndallisation: exposure to steam at 100°C, used for sugar & gelatin media, 20 min for 3 successive days to kill spores.  26 STERILIZATION AND III. Temp above 1000 C DISINFECTION 1. Autoclave: Principle- water boils when it’s vapour pressure equals the surrounding atmosphere. Pressure inside a closed vessel is made to rise, so water boils at higher temp, releasing steam. Steam has good penetrating power & condenses to give up it’s latent heat to the article, creating a vacuum, drawing in more steam to the area till temp of the surface is raised to that of steam.  27 STERILIZATION AND DISINFECTION May be vertical or horizontal cylinder with a steam jacket (water compartment). Made up of gunmetal/ stainless steel. The lid is made airtight with screw clamps & asbestos washer. Upper side consists of: i. Discharge tap for air & steam ii. Pressure gauge iii. Safety valve Heating is done electrically.  28 STERILIZATION AND Used to sterilize DISINFECTION 1. All critical & semi-critical items that are heat & moisture resistant. 2. Surgical instrument, anesthetic equipment, dental instruments, implanted medical devices, surgical drapes, linens. 3. For sterilization of various culture media & aqueous solutions. 4. Surgical dressings. 5. Pharmaceutical products. 6. Discarding cultures (biohazardous waste). 7. Autoclavable plastic containers.  29 STERILIZATION AND Method of operating autoclave DISINFECTION Water level is adjusted, articles are placed on perforated tray, lid is closed & autoclave is switched on. Conditioning phase - Safety valve is adjusted to required pressure. - Discharge tap is closed after complete removal of air. - After desired pressure is reached (15 lbs psi), the safety valve opens & excess steam escapes. Exposure phase - From this point holding time is calculated (15 mins). Exhaust phase - It is switched off & allowed to cool till pressure inside is equal to that of the atmospheric pressure & discharge tap is opened & air is let into autoclave.  30 STERILIZATION AND DISINFECTION Precautions Discharge tap should not be opened when inside pressure is still high because it may lead to violent boiling of the liquid media & spillage or explosion. If it is opened after the inside pressure has fallen below atmospheric pressure, an excessive amount of water would have evaporated & lost from the media.  31 STERILIZATION AND DISINFECTION Sterilization conditions- Temp/ time cycle 1210C for 15 min 1260C for 10 min 1340C for 3 min  32 STERILIZATION AND DISINFECTION  Sterilization controls 1. Biological indicator - Geobacillus stearothermophilus (thermophile) is used to test efficacy of sterilization by moist heat. - Its spores grow at 55- 600C & require an exposure of 12 mins at 1210C to be killed. - Paper strips impregnated with 106 spores are placed in paper envelops kept in lowermost & innermost parts of the load. - After sterilization, the strips are inoculated into suitable medium & incubated at 550C for 5 days. - If spores germinate & color of media changes from purple to yellow then it is proved that sterilization is improper.  33 STERILIZATION AND DISINFECTION Unsterilized tube Sterilized tubes  34 STERILIZATION AND 2. Chemical indicator DISINFECTION - Autoclave tape: a heat sensitive material which undergoes color change if sterilization parameter is achieved - Put on the external surface of each pack to indicate that the pack has been directly exposed to sterilization method  35 STERILIZATION AND DISINFECTION Filtration Performed for heat sensitive liquids- serum, sugars & antibiotic solutions. Only bacteria is removed. There are two types of filters: 1. Depth filters 2. Membrane filters  36 STERILIZATION AND DISINFECTION 1. Depth filters Porous filters that retain particles throughout the depth of filter. Made up of mats of metallic, polymeric or inorganic material. Rely on density & thickness of filter to trap particles. Egs. Candle filters. - Unglazed porcelain. - Asbestos filters. - Sintered glass filters.  37 STERILIZATION AND DISINFECTION Uses: - Industrial applications. - Food, beverages & chemicals. Advantages: 1. Can retain a large mass of particles before becoming clogged. 2. Flow rate of fluid is high. 3. Low cost. Disadvantages: 1. Some of the particles still come out of filtrate. 2. Not suitable for filtration of solution containing bacteria.  38 STERILIZATION AND DISINFECTION 2. Membrane filters Made up of cellulose nitrate, polyvinylidene chloride & have pores of uniform & predetermined size. Most common method for use in hospitals, sterility testing & for preparation of solutions for parenteral use. Average pore size of 0.22 µm removes most bacteria allowing viruses to pass through.  39 STERILIZATION AND DISINFECTION  40 STERILIZATION AND 1. Air filters: surgical masks & HEPA filters DISINFECTION a. Surgical masks- (3 ply mask)- polypropylene filter layer in between 2 layers of non woven fabric. b. Large volumes of air can be rapidly freed from infective agents by passage through high efficiency particulate air (HEPA) filters which remove 99.97% particles of 0.3µ or larger. Used in Biosafety cabinets, OTs. - ULPA filter: Ultra low particulate air filter can remove at least 99.999% of dust, pollen, mold, bacteria & any air borne particles with a size of 0.12µm or larger  41 STERILIZATION AND DISINFECTION Liquid filtration - Used for bacteriological examination of water in hospital settings - dialysis water. - To remove bacteria from pharmaceutical fluids that are heat labile & cannot be purified by any other means. - Sterilisation control: a. Brevundimonas diminuta. b. Serratia marsecens.  42 STERILIZATION AND Radiation DISINFECTION 1. Non ionizing radiation interferes with DNA replication but do not penetrate glass, dirt films water etc. a. Infrared- rapid, mass sterilization of pre-packed items (syringes, catheters), serum, vaccines, toxins. b. Ultraviolet- enclosed areas like OTs, labs, inoculation hoods, biosafety cabinets in which dangerous microorganisms are handled & also in sterilization of drinking water. - The recommended dose is 250- 300nm wavelength of UV rays for 30 minutes.  43 STERILIZATION AND DISINFECTION 2. Ionizing (cold sterilization) - X-rays, Gamma rays (from cobalt 60)- very high penetrative power & causes breakage of DNA but temp is not increased. - They induce structural defects in microbial DNA, inhibit DNA synthesis, leading to cell death. - Used for- Disposable rubber or plastic syringes, tissue for transplant, phamaceuticals, catheters, metal foils, oils, gloves that are unable to withstand heat. - Sterilisation control: Bacillus pumilus.  44 STERILIZATION AND DISINFECTION Incineration Used for treatment of Bio-medical waste materials. It burns waste at a very high temperature 870- 1,200°C converting into ash.  45 STERILIZATION AND DISINFECTION Microwave For disinfection of soft contact lenses, dental instruments, dentures, urinary catheters. MOA: Microwaves are radio-frequency waves, which are (2450 MHz); produce friction of water molecules which generates heat.  46 STERILIZATION AND DISINFECTION Disinfectants  47 STERILIZATION AND DISINFECTION Chemical disinfectants Destroys microorganisms by chemical or physicochemical means Different organisms vary in their sensitivity. ▫ Gram-positive - highly sensitive. ▫ Gram-negative - relatively resistant. ▫ Clostridial & mycobacterial species - very resistant. ▫ Slow viruses - highly resistant. Disinfectants are suitable for heat-sensitive items. Less effective than heat. Chemicals used include: ▫ Clear soluble phenolics. ▫ Hypochlorites. ▫ Alcohols. ▫ Quaternary ammonium compounds.  48 STERILIZATION AND DISINFECTION High- level disinfectants (HLD) Kill bacterial spores when used in sufficient concentration under suitable conditions. 1. Aldehyde- Formaldehyde, glutaraldehyde, ortho-phthalaldehyde MOA- They combine with nucleic acids, proteins, inactivate them by cross- linking & alkylating molecules.  49 Glutaraldehyde Ortho-phthalaldehyde Formaldehyde STERILIZATION AND Uses Uses ™ ses U : ™ 1. Semicritical items- 2% or 1. Semicritical items- 0.55 % DISINFECTION 1. preservation of ™ 2.4%A(e.g. dvantages: Cidex) Disinfection time- 5-10 min anatomical specimen Disinfection time- 20 min 2. Preservation of stool ™ (forDspores isadvantages: 10- 14 hrs) specimen 2. Fogging, cleaning of floor 3. embalming agent & surfaces of critical areas (e.g. Bacillocid Extra) Advantage- It remains active Advantages- it does not require in the presence of organic activation, better odor, less eye matter, has excellent material irritation, acts faster (5- 10 min) compatibility Disadvantage- It has a Disadvantage- does not kill spores Disadvantage- Produces pungent odour, can produce effectively, stains skin gray irritating fumes, pungent eye irritation, occupational odor, potential asthma, contact dermatitis carcinogen, corrosive to metals, skin irritation, asthma  50 STERILIZATION AND DISINFECTION 2. Peracetic Acid Used in automated machines or as manual immersion; 0.1- 0.2%, used for 5- 15 min. Use- endoscopes, arthroscopes, surgical, dental instruments. ™Disadvantages- Expensive, has material compatibility issues, causes chemical irritation, eye damage. 3. Hydrogen Peroxide (H2O2) MOA- hydroxyl free radicals that attack various cell components.  51 STERILIZATION AND DISINFECTION Uses: - Sporicidal only at >4- 5% - 3% is used for environmental surface disinfection, fogging, for wound cleaning - 3- 6% to disinfect soft contact lens, tonometer biprisms, ventilators, fabrics, and endoscopes, etc. - 6- 7.5% as chemical sterilant in plasma sterilization. - Vaporized H2O2 is used for industrial sterilization of medical devices and for decontamination of areas. Advantages: rapid action, nontoxic, has detergent properties with good cleaning ability, is active in presence of organic material. ™ Disadvantages: expensive, has material compatibility issue, chemical irritation, corneal damage.  52 STERILIZATION AND DISINFECTION Potassium permanganate (KMnO4) is a red crystalline powder that colours everything it touches, and is used to disinfect aquariums. It is also used widely in community swimming pools to disinfect ones feet before entering the pool. Typically, a large shallow basin of KMnO4/water solution is kept near the pool ladder. Participants are required to step in the basin and then go into the pool. Additionally, it is widely used to disinfect community water ponds and wells in tropical countries, as well as to disinfect the mouth before pulling out teeth. It can be applied to wounds in dilute solution; potassium permanganate is a very useful disinfectant.  53 STERILIZATION AND DISINFECTION Intermediate-level disinfectants 1. Alcohol MOA: kill all microorganisms except spores by denaturation of proteins. Uses: Alcohol (60- 80%) is used for various purposes. - ™ Alcohol based handrub (ABHR). - Disinfecting smaller non-critical instruments (thermometers), which are immersed in alcohol for 10–15 minutes. - ™ Disinfection of small medical items/surfaces such as rubber stoppers of multiple-dose medication vials or vaccine bottles and hubs of the central line.  54 STERILIZATION AND DISINFECTION - Disinfection of external surfaces of equipment such as stethoscopes, ventilators, manual ventilation bags, ultrasound machines. - ™ Disinfection of non-critical surfaces such as laboratory bench, medication preparation areas. - Spirit (70% alcohol): Used as skin antiseptic. Disadvantages Flammable and must be stored in cool, well-ventilated area. Evaporate rapidly, making exposure time difficult to achieve unless the items are immersed. May damage tonometer tips, lenses. Inactivated by organic matter.  55 STERILIZATION AND DISINFECTION 2. Phenolics (carbolic acid) Phenol was the first widely used antiseptic & disinfectant for surgery in 1867 by Joseph Lister (the father of antiseptic surgery). MOA: protoplasmic poison, disrupt cell wall, precipitate cell proteins. Uses - Cresol, lysol for disinfecting environmental surfaces (e.g. bedside tables, bedrails, laboratory surfaces) & noncritical medical devices. - 5% phenol is mycobactericidal used for disinfection of sputum specimen - Used as antiseptics: chloroxylenol. ™. Advantages: Phenolics retain activity in presence of organic materials. ™Disadvantages: They can cause hyperbilirubinemia in infants, toxic to skin.  56 3. Halogens STERILIZATION AND DISINFECTION 1. Iodine MOA- disruption of protein & nucleic acid. ™. a. Tincture of iodine: iodine (2%) in potassium iodide, can cause staining, skin allergy. b. Iodophor (e.g. povidone iodine): It is prepared by complexing iodine with carrier (povidone) which helps in sustained-release of iodine. It is nonstaining, no skin toxicity. - Used as antiseptics 5 % topical solution and ointment is used for wound cleaning. 7.5% is used for hand scrub. 10% is used for surgical skin preparation. 1% is used as an oral antiseptic, for mouth wash. - Used as disinfectant for medical equipment, such as hydrotherapy tanks, thermometers.  57 STERILIZATION AND DISINFECTION 2. Chlorine & Hypochlorite Preparations: - Liquid form (sodium hypochlorite or household bleach). - Powder form (calcium hypochlorite or bleaching powder). - Other forms: include sodium dichloroisocyanurate (NaDCC) available as tablets & chlorine dioxide. MOA: All preparations yield hypochlorous acid (HClO), which causes oxidation of cellular materials, destruction of vegetative bacteria/ fungi.  58 STERILIZATION AND DISINFECTION Uses (free chlorine): used for disinfection of municipal water supplies & swimming pool water. Uses (sodium hypochlorite): available at 5.25- 6.15% (50,000 ppm of available chlorine); contact time 10- 20 min. - Large blood spill: 0.5% (1:10 dilution or 5,000 ppm). - Small blood spill: 0.05% (1: 100 dilution, or 500 ppm). - Pre-treatment of liquid waste before disposal: 1% (1:5 dilution, 10,000 ppm). - Laundry items : 0.1% (1 in 50 dilution 1,000 ppm. ™ - Surface disinfectant: 0.5% (1:10 dilution or 5,000 ppm). - C. difficile (diarrheal stool): Hypocholorite is sporicidal only >0.5% (5000 ppm).  59 STERILIZATION AND DISINFECTION Advantages: - Hypochlorites are broad spectrum, rapid in its action, non-flammable, low cost. ™isadvantages: D - Inactivated by organic matter. - Toxic to skin/ mucosa, carcinogenic. - Daily preparation. - Corrosive, damages fabrics, carpets. - Leaves residue, requires rinsing or neutralization. - Offensive odors. - Bleaches the fabrics & carpets.  60 STERILIZATION AND DISINFECTION 4. Heat-based Methods 1. Pasteurization: Developed by Louis Pasteur, used to disinfect respiratory/ anesthesia equipment, by immersing in hot water (70°C for 30 min) 2. Boiling at 100°C. 3. Steaming at 100°C: When the autoclave is used without closing the pressure valve, the temperature does not rise beyond 100°C. It may be useful for disinfecting those items which cannot withstand high temperature of autoclave. 4. Inspissation: egg-based culture media such as Lowenstein- Jensen medium are sterilized by heating at 80- 85°C for 30 min on 3 successive days to kill spores.  61 STERILIZATION AND DISINFECTION 5. Ultraviolet (UV) Radiation MOA: Non ionizing radiation, destroys nucleic acid through induction of thymine dimers, kills most microorganisms; not spores. Uses: - Disinfection of drinking water, titanium implants & contact lenses. - Disinfection of air and/or surfaces as in operating rooms, isolation rooms, biologic safety cabinets. Disadvantages: - Effectiveness influenced by organic matter. - In isolation rooms, it may cause skin erythema & keratoconjunctivitis in patients. UV lamps should be placed at least above 2-meters height from the floor level.  62 STERILIZATION AND DISINFECTION Low-level disinfectants Destroy vegetative bacteria, enveloped viruses, variable action on nonenveloped viruses, fungi, no action on tubercle bacilli/ spores. 1. Quaternary Ammonium Compound (QAC) MOA: inactivation of energy producing enzymes, denaturation of essential cell proteins, disruption of cell membrane. Use: environmental sanitation of noncritical surfaces, such as floors, furniture, walls, non-critical medical equipment that contacts intact skin (BP cuffs). Eg. Benzyl ammonium chloride, didecyl dimethyl ammonium bromide.  63 STERILIZATION AND DISINFECTION 2. Chlorhexidine Gluconate (CHG)- biguanide disinfectant MOA: acts by disruption of cytoplasmic membrane. Uses: ™ - Hand hygiene product: Hand rub (0.5%), hand wash (4%). - Mouthwash (0.1- 0.2%). - Body wash solutions Skin disinfectant before surgery (2%). - Antiseptic for wound cleaning. Advantages: residual activity, less irritant. Disadvantages: slower action, activity is pH dependent, greatly reduced in presence of organic matter, dermatitis on prolonged use.  64 Cleaning Products STERILIZATION AND DISINFECTION Enzymatic (proteolytic) cleaners- enzymes such as amylase, lipase, cellulase, protease which break down proteinaceous matter present on equipment. Cleaning chemicals (detergents)- act by reducing surface tension, dissolving fat, organic matter; detergents used for surface, floor cleaning are different than that used for instrument cleaning. Cleaning Methods - Manual cleaning: by immersion of instruments into cleaning solution, or by wiping surfaces with cloth soaked with cleaning solution. - Automatic or mechanical cleaning: useful for cleaning hard-to-reach parts of surgical instruments. Egs. ultrasonic washers. Cleaning followed by disinfections: Cleaning: Always cleaning with a detergent is performed first, before applying disinfectant.  65 STERILIZATION AND DISINFECTION thanks