Sterilization and Disinfection 1.ppt.pdf PDF

STERILIZATION AND DISINFECTION Objectives: At the end of the lecture presentation students should: 1) Be able to appreciate the importance of “moist heat” and “dry heat” sterilization used in the hospital environment 2) familiar with the types and mode of action of disinfecBecome ting agents, with p...

STERILIZATION AND DISINFECTION Objectives: At the end of the lecture presentation students should: 1) Be able to appreciate the importance of “moist heat” and “dry heat” sterilization used in the hospital environment 2) familiar with the types and mode of action of disinfecBecome ting agents, with particular reference to medical diagnostic laboratories, hospital wards and theatres STERILIZATION AND DISINFECTION Objectives cont’d: 3) Become familiar with the appropriate choice of disinfectants used for critical and non-critical items used in the hospital environment STERILIZATION AND DISINFECTION DEFINITIONS ▪Sterilization – removal of all viable micro-organisms including bacterial and fungal spores ▪Disinfection – removal or killing of disease causing microorganisms ▪Bactericidal – kills bacteria ▪Bacteriostatic – inhibits growth of bacteria ▪Antiseptic – substance used on/or in living tissues for inhibiting or destroying micro-organisms ▪Asepsis – prevention of access of micro-organisms to materials PHYSICAL METHODS OF STERILIZATION DRY HEAT a) Hot air oven ---Temp. 1600c –1800c for 1 hour ---main means of dry heat sterilization b) Flaming--- direct exposure for a few seconds in a gas or spirit flame c) Red heat---holding inoculating wires, forceps and spatulas until red hot d) lncineration--- total destruction by burning. e) Infra-Red Radiation--- Infra-Red rays are directed from an electrically heated element onto the objects to be sterilized. -> 2000 c by Infra-Red in vacuo is employed in sterilization of surgical instruments. HOT AIR STERILIZER MOIST HEAT - Cheaper, quicker and more efficient - Includes boiling, live steam and steam under pressure - Uses temperatures of 1) < 1000c, 2) 1000c, 3) > 1000c AUTOCLAVING - Uses saturated steam under pressure - Sterilization ensured at a temp.0c of 1210c for 15 minutes at 15 lbs pressure - Kills micro-organisms including spores - Widely used for sterilization of surgical supplies and bacteriological culture media AUTOCLAVE CONTROL 1) Temperature record 2) Thermocouple 3) Indicators – a) Chemical - Bowie Dick Autoclave Tape, Brownes Tubes b) Biological – spore strips eg. Bacillus stearothermophilus AUTOCLAVES STANDING TABLE TOP STEAM-JACKETED AUTOCLAVE 5 6 3 2 4 1 INDICATIONS OF STERILIZITION Bowie Dick Method (Satisfactory run) Completed Sterilization Bowie dick showing dark colour change UNSATISFACTORY RUN COLOUR CHANGE INCOMPLETE AT CENTRE ( BOWIE DICK TAPE ) PASTEURIZATION - ensures the destruction of non-spore forming organisms eg. Mycobacteria ( M. bovis ), Coxiella burnetti may survive The holder method: 630c – 660c for 30 minutes The flash method: 720c for 20 seconds BOILING Vegetative organisms are killed at 1000c for 10 minutes Does not ensure sterility Used for treatment of bowls and instruments for wards and theatres TYNDALLIZATION Intermittent exposure (steaming) for 20 – 45 minutes on each of 3 successive days. 1st day – vegetative organisms destroyed 2nd day – germinated spores killed 3rd day – precautionary measure - used for culture media containing sugar, serum and gelatin that will decompose at high temperature. STEAMING - Single exposure for 90 minutes at 1000c ( spores may survive ) - Vaccine preparation: 600c for 1 hour OTHER PHYSICAL METHODS FILTRATION FILTRATION Mechanical sieving - Mechanical sieving - Principal method for sterilization of heat labile materials eg. serum, toxin Filters - seitz filter (compressed asbestos) - sintered glass filter (Berkefield) - millipore filter - bacteria, fungi and extraneous materials are held back Filtration of air - cotton wool plug used in tubes (allows sterile air to enter) - larger and more elaborate filters are used to provide sterile air for operating theatres Filter Assembly Syringe Filters ELECTRON MICROGRAFT OF STAPHYLOCOCCUS EPIDERMIDIS ON THE SURFACE OF A 0.22 µm MILLIPORE MEMBRANE FILTER RADIATION Uses varying wavelengths for sterilizing heat labile materials a) Ultraviolet light - wavelengths between 250 and 270 nm are absorbed by nucleic acids - denatures proteins and nucleic acids - used to reduce the number of micro-organisms in air in operating theatres and animal rooms b) Gamma radiation and X - rays - ionizing radiation - denatures proteins and nucleic acids - used to sterilize plastics, pharmaceutical products and to preserve foods. c) Microwave radiation - absorbs water molecules , then releases microwave energy to surroundings as heat. MICROWAVE STERILIZATION CHEMICAL STERILIZATION ETHYLENE-DIOXIDE GAS – expensive, time consuming and dangerous ( explosive ) - used in hospitals for sterilizing machines and plastic products and other surgical materials DISINFECTANTS WHICH CAN BE USED TO ACHIEVE STERILIZATION (Dependent on exposure time and concentration) Glutaraldehyde - concentration variable Hydrogen peroxide - 6 to 30% Formaldehyde - 6 to 8% Chlorine dioxide - concentration variable Peracetic acid - concentration variable DISINFECTION -Includes nonselective chemicals -Controls the growth of micro-organisms on inanimate objects ( disinfectants ) in human tissue (antiseptics ) -Ideally should be soluble in water -Have a low toxicity for humans -Should be reasonably economical TYPES OF DISFECTANTS 1) AGENTS THAT DAMAGE CELL MEMBRANE Surface active agents -reacts with lipid in cell membrane Include a) Anionic – strong detergents, weak antimicrobials eg. soaps, fatty acids a) Anionic agents cont. - most active at acid pH - effective against Gram positive organisms and moderately effective against Gram negative b) Cationic - most important surface active agents eg. Quaternary ammonium compound (QAC) - strong bactericidal ( at high conc. ), weak detergent - sporostatic, fungistatic (except for tricophyton ) - active against viruses with lipid envelopes - most active at alkaline pH c) Non- ionic - make cell wall fragile eg. Tween 80 d) Ampholytic - properties of anionic and cationic ( detergent + antimicrob. ) 2) AGENTS THAT DENATURE PROTEINS Include: - acids, alkalis, alcohols, acetones and other organic solvents - antimicrobial activity by altering the pH of the organisms environment Acids eg. Lactic, benzoic, propionic, sorbic ( food aditives/preservitives ) - HCL (25%) – disinfecting hides and skin with anthrax spores Alkalis eg. – NaOH , caustic soda ( kills vegetative forms ) Alcohols - water is essential for activity ( 60% to 70% alcohol ) - bactericidal, act poorly against viruses Ethanol – used to sterilize skin and to disinfect clinical termometers 3) AGENTS THAT MODIFY FUNCTIONAL GROUPS OF PROTEINS AND NUCLEIC ACIDS Heavy metals - precipitate proteins and other organic molecules eg. Silver nitrate, copper sulphate and merbromin ( mercurochrome ) are widely used as antiseptics Silver nitrate (5%) - bactericidal for Neisseria gonorrhoeae Silver sulfadazine - topical application for burn cases Oxidizing agents - inactivate enzymes eg. Halogens – chlorine, iodine ( widely used as antiseptics and disinfectants ) Chlorides – actively increases with concentration Household bleach ( 5.5% NaOCL __ Sodium hypochlorite) - sporicidal, effective against viruses Iodine – common antiseptic for cuts and burns AGENTS THAT MODIFY FUNCTIONAL GROUPS OF PROTIENS AND NUCLEIC ACIIDS CONT. Phenols and substituted derivatives - denature proteins and disrupt cell membrane - highly effective disinfectants ( wide range of organisms including Mycobacteria) - low concentrations are used as antiseptics - phenolic derivatives eg. carbolic acid , lysol Alkylating agents - bind sulfhydryl or amino acid group eg. Glutaraldehyde, formaldehyde Glutaraldehyde - 10 times more effective than formaldehyde - used as a 2% concentration - effective against bacteria, spores, fungi and viruses eg. HIV Alkylating agents cont. - not inactivated by organic matter - not corossive to metal, rubber and plastic - used to disinfect critical items used in invasive procedures eg. endoscopes Formaldehyde - liquid ( 34% - 38% ) and gaseous state - lethal to bacteria and viruses - used for preserving tissues, embalming fluid - used as a fumigant or gas to decontaminate rooms, buildings, fabric and instruments HIGH LEVEL DISINFECTION Method of choice for critical and semicritical items Include : 1) 2% activated glutaraldehyde 2) 6% hydrogen peroxide 3) 3-8% formaldehyde Glutaraldehyde - available as a 2% buffered glutaraldehyde solution - a chemo-sterilizer - broad spectrum activity : bactericidal , fungicidal, virucidal sporicidal - exposure time: bacteria and viruses – 30 min. at rt. Oc, spores – 6 hours - used for medical instruments ( scalpel ), endoscopes, other items which cannot be sterilized by steam or autoclaving.