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STERILISATION AND DISINFECTION

STERILISATION AND DISINFECTION. DO THEY SOUND SIMILAR. ARE THEY ACTUALLY SIMILAR. WHAT IS THE DIFFERENCE?. DEFINITIONS. STERILISATION: process by which an article, surface or medium is made free of all living organisms either in the vegetative state or in the spore state . DISINFECTION:

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STERILISATION AND DISINFECTION

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  1. STERILISATION AND DISINFECTION

  2. DO THEY SOUND SIMILAR

  3. ARE THEY ACTUALLY SIMILAR

  4. WHAT IS THE DIFFERENCE?

  5. DEFINITIONS • STERILISATION: • process by which an article, surface or medium is made free of all living organisms either in the vegetative state or in the spore state. • DISINFECTION: • Process that destroys most of the pathogenic organisms but not spores

  6. DEFINITIONS • ASEPSIS: • Process where chemical agents are applied onto the body surface which kill or inhibit the microbes present on the skin • DECONTAMINATION: • reduction of pathogenic microbial population to a level at which items are considered safe to handle without protective attire.

  7. DEFINITIONS • -CIDAL agents: • Agents which can kill microorganism. • -STATIC agents: • Agents which inhibit the microbial growth.

  8. History of sterilisation • Embalming • Use of fire and chemical to purify the environment. • Pasteur’s work on dry heat sterilizers. • Your mother sterilising all the woollen clothes in sun to be keep them ready for the next winters • Your grandmother drying all the glass utensils in hot sun before storing the pickle in it.

  9. METHODS OF STERILISATION PHYSICAL METHODS CHEMICAL METHODS Alchohols Aldehydes Phenolic compounds Biguanides Halogens Oxidising agents Heavy metal salts Surface active agents Dyes Gaseous sterilisation • Drying • Heat • Dry heat • Flaming • Incineration • Hot air oven • Moist heat • Below 100o C • At 100o C • Above 100o C • Filtration • Radiation • Ultrasonic waves

  10. PHYSICAL METHODS • Drying: • Moisture….. • Drying ….. • But…… • Do not affect many microbes including spores.

  11. B. Heat: • Most reliable • Commonly used method • Considered method of choice unless contraindicated • 2 types of heat are used in sterilisation processes. • Dry heat • Moist heat

  12. Dry heat: • Mechanism of action: Kills the organism by • Charring • Denaturation of bacterial proteins • Oxidative damage • Elevated level of electrolytes • Flaming: • Items are held in bunsen flame for a long period till they become red hot (inoculating wires, loops forcep tips etc) or a short duration (for fragile items like mouth of test tubes).

  13. Incineration: • Used for disposal of BMW • Burns anatomical and microbiological waste • At a temperature of 870o C to 1800o C • Converts it into ash, gas and heat.

  14. Hot air oven • Widely used dry heat method. • Was originally devised by Pasteur. • Made up of double jacket chamber. • Has perforated trays inside. • Is fitted with a thermometer, a thermostat and a fan. • Has outlets for removing the vapour generated during the process. • Has a temperature setting knob and a time setting knob.

  15. Holding temperature: 160o C • Holding time: 2 hours • Materials which can be sterilised by hot air oven are: • Glassware • Metal Surgical instruments • Powders like starch, zinc oxide etc • Glycerol, liquid paraffin, fats, oil.

  16. Precautions: • Do not overload. • Arrange the material to allow free circulation of air. • Materials should be dried completely. • Close the mouths of test tubes, flasks etc with cotton plugs. • Items should be wrapped in paper • Inflammable material should not be placed inside the chamber • Allowed to cool before opening as sudden cooling may crack the glassware.

  17. Advantages of dry heat sterilization • A dry heat cabinet is easy to install and has relatively low operating costs; • It penetrates materials • It is nontoxic and does not harm the environment; • And it is noncorrosive for metal and sharp instruments. • Disadvantages for dry heat sterilization • Time consuming method because of slow rate of heat penetration and microbial killing. • High temperatures are not suitable for most materials • The time and temperature required will vary for different substances and overexposure may ruin some substances.

  18. Sterilisation control: • Done to check the effectiveness of the sterilisation process. • Can be monitored by • Biological indicator: 106 spores of bacillus atrophaeus are used now a days • Earlier spores of clostridium tetani were used. • Physical control- digital display

  19. Moist Heat Methods • Below 100 C • Pasteurisation • Inspissation • Vaccine bath • At 100 C • Boiling • Tyndallisation • Steam sterilisation • Above 100 C- Autoclave

  20. Principle • When water boils its vapour pressure equals to that of surrounding atmosphere • When atmospheric pressures increases • Boiling temperature also increases

  21. Parts of an autoclave • Pressure chamber: large cylinder made up of gunmetal or stainless steel • A steam jacket • Lid which is fastened by screw clamps • Lid has discharge tap, pressure guage and safety valve • Electrical heater is attached to the steam jacket

  22. Working • Cylinder filled with sufficient water • Material placed in pressure chamber • Lid closed and heater is switched on • Safety valve adjusted to the required pressure • After water boils, air+ steam mixture allowed to escape through discharge tap • When steam pressure reaches the desired level, safety valve opens, excess steam released

  23. Holding period is counted from this point • At pressure 15 psi, the holding temperature is 121 C and holding period is 15 mins. • After the holding period, heater switched off • Autoclave allowed to cool till pressure guage indicates the pressure inside equals atmospheric pressure • Discharge tap open • Air enters the autoclave • Lid opened and sterilized material removed.

  24. precautions • Not to be used for waterproof material • Loaded in such a way that efficient steam penetration occurs • Materials should not touch the sides or top of chamber • Clean items and waste to be autoclaved seperatly.

  25. Uses • Surgical instruments • Culture media • Plastic containers • Glassware

  26. Sterilisation control • Biological indicator: Spores of geobacillusstearothermophilus • Brownes tube • Thermocouplers • Autoclave tape

  27. Filtration • Remove microbes from solutions of heat labile materials. • 2 types: • Depth filters- retain particles throughout the depth of the filters • Retain a large mass of particles, fluid floe rate is high, cost is low. • Disadv: some particles may come out in filtrate.

  28. Membrane filter: porous, retain particles on surface. • Made up of cellulose nitrate, cellulose acetate • Average pore size is 0.22um, removes most of the bacteria

  29. Uses of filtration • Filtration of liquids • Sera, sugar, antibiotic solution • Separation of toxins from bacteria • Bacteria free filtrates for virus isolation • Purification of water • Filtration of Air: • Surgical masks • HEPA filters • ULPA filters

  30. Radiation • Ionising radiations: • X rays, gamma rays • Breakage of DNA withod increasing the temperature • Aka cold sterilisation • Penetrates deep • Destroys spores, not always effective against viruses

  31. Uses of ionising radiations: • Disposable plastic supplies • Catgut sutures, bone and tissue grafts, adhesive dressings • Antibiotics and hormones • Irradiation of food

  32. Non ionising radiation • Infrared and UV rays • Lethal but penetration power is very low • So not used commonly • 250-300nm wavelength for 30 mins • Used for disinfection of clean surfaces in OT, laminar air hoods, water treatment. • Burns the skin and damages the eyes

  33. Ultrasonic waves • Disrupt the bacterial cell wall.

  34. DISINFECTION • Def: • Agents called as disinfectant • Based on their microbicidal activity they are classified into 4 groups: • Low level disinfectants • Intermediate level disinfectants • High level disinfectants • Chemical sterilants

  35. Mechanism of action of disinfectants • They act by any one of the following mechanism: • Damage cell wall and alter permeability • Alter proteins and form salts or cause coagulation • Inhibit enzyme action • Inhibit nucleic acid synthesis • Cause oxidation or hydrolysis.

  36. Factors influencing activity of disinfectant 1. Organism load- 2. Type of microorganism- 3. Physiological state of cell- 4. Nature of the agent of disinfection- 5. Time of exposure- 6. Environment-

  37. Ideal disinfectant • Wide spectrum of activity • Act in presence of organic matter • Non toxic, non corrosive • Stable • Odourless • Soluble in water and lipid • Effective in acidic as well as alkaline pH • Rapid action • Inexpensive

  38. Types of disinfectants • Alchohols: most widely used • Low level disinfectants • Ethanol and isopropyl alchohol in 70-80% concentration. • Denature protein and dissolve lipid in the membranes. • Ethanol- surgical spirit. • Isopropyl alchohol-clinical thermometers soaked for 10-15 mins.

  39. Aldehydes: • Formaldehyde, glutaraldehyde(2%), ortho-phthaldehyde • Combine with nucleic acid proteins and inactivate them. • Sporicidal. So can be used as chemical sterilant. • Formaldehyde:40 % widely used preparation • Dissolved in water or alcohol before • Used for preserving anatomical specimen • Fumigation of closed areas • Toxic , irritant and corrosive

  40. Glutaraldehyde • Less toxic • Less irritant • Less corrosive • Used in 2% concentration • Commercially available as cidex • 20 mins to disinfect an object • May kill spores on longer exposure • Available in inactive form. • Stable only for 14 days • Used for sterilisation of Endoscopes and cystoscope.

  41. Ortho- phthaldehyde: • Used in 0.55% concentration • Advantages over glutaraldehyde • Doesnot require activation • Better odour • Low vapour property • Stable • Increase mycobactericidal activity

  42. Phenolic compounds: • Introduced by Joseph Lister • First most widely used antiseptic and disinfectant • Produced by distillation of coal tar • Act by denaturing proteins and disrupting cell wall • They have mycobactericidal activity • Are effective in presence of organic matter. • As Disinfectant: • Lysol, cresol, xylenol • Toxic and irritant to skin • As Antiseptics: • less irritant, persists for longer time, more active against gram positive bacteria

  43. Halogens: • Iodine: • Skin antiseptic • Can kill spores at higher concentratyin • Used in 2 forms • Tincture iodine- 2% in water-ethanol solution of KI • Effective but can cause skin allergy • Iodophor-iodine +organic carrier like povidone • Water soluble, stable, non staining • Causes slow release of iodine so minimizes side effects.

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