1. STERILISATION AND DISINFECTION
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2. STERILISATION Sterilisation
A process by which an article, surface or medium is free of all living organisms either in vegetative state or spore state
Disinfection
Removal or destruction of all pathogenic organisms
Asepsis
Prevention of infection by inhibiting the growth of bacteria

3. STERILISATION Cleaning
Removal of soil and dirt to reduce microbial burden and to make sterilisation more effective
Decontamination
The process of rendering an article or an area free of contamination including microbial, chemical, radioactive, etc.
Bactericidal agents: Agents that kill bacteria
Bacteriostatic agents: Agents that prevent multiplication of bacteria

4. STERILISATION
Objective: To destroy microorganisms from materials and areas Choice of method depends on: Purpose for which it is carried out, nature of microorganisms, material to be sterilised Uses of sterilisation: To prevent contamination by extraneous organisms, to prevent sepsis in surgery, for safety in food and drugs

5. CLASSIFICATION Physical methods Sunlight, drying, dry heat - flaming
- incineration, hot air oven
Moist heat
- Pasteurisation, boiling
- Steam under normal pressure
- Steam under pressure
Filters, radiation
Ultrasonic and sonic vibration

6. CLASSIFICATION Chemical methods
Alcohols - Ethyl alcohol, isopropyl alcohol
Aldehydes - Formaldehyde, glutaraldehyde
Dyes
Halogens
Phenols
Surface active agents
Metallic salts
Gases: ETO, formaldehyde, betapropiolactone

7. DRY HEAT

8. FLAMING
Flaming: Inoculating loops, wires, tip of forceps, edges of test tubes
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9. HOT AIR OVEN Holding period – 160°C for 1 hour
- Glassware, instruments, liquid paraffin, dusting powder, fats, grease, etc.
- Rubber, cotton avoided
Controls - C.tetani spores and Browne’s tubes

10. HOT AIR OVEN
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Hot air oven

11. INCINERATION
Contaminated cloth, animal carcasses, pathological materials, infectious hospital waste

12. STERILISATION CONTROL
Physical
Temperature monitoring and thermocouples
Chemical
Browne’s tube (green spot)
Biological
Non-toxigenic strain of Clostridium tetani or Bacillus subtilis
Paper strips impregnated with 106 spores inserted in pack to be sterilised

13. MOIST HEAT Temp <100°C Pasteurisation
– Holder method- 63°C – 30 min
– Flash method – 72°C – 20 sec
Followed by quickly cooling to 13°C
Vaccine bath: Heat inactivation – 60°C – 1 hr
Inspissation: 80–85°C 30 min on 3 days

14. MOIST HEAT Temperature at 100°C Boiling
Koch & Arnold steam steriliser: media –90 min
Tyndalisation: sugars, gelatin
100°C – 20 min - 3 successive days

15. STEAMER
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Steamer

16. MOIST HEAT Temp >100°C : (Steam under pressure) Autoclaves
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A simple autoclave; 1. release valve; 2. safety valve; 3. pressure gauge; 4. tightening screws; 5. cover; 6. body; 7. bin containing material; 8. heating element; 9. stand

17. STERILISATION CONTROL
Physical
Temperature and pressure monitoring gauges, thermocouples
Chemical
Bowie–Dick tapes
Biological
Bacillus stearothermophilus 106 spores

18. FILTRATION
- Heat labile fluids - sera, antibiotics, enzymes, toxins
- Separation of virus from bacteria
Types of filters:
Candle filters
Berkfeld & Mandler: Made of kieselghur, graded porosity, sterilised by steaming or autoclave
Chamberland or Doulton: Made of unglazed ceramic

19. FILTERS Asbestos filters:
Seitz filter: - pad of asbestos - inserted into metal holder - discarded after use
Asbestos filter

20. FILTERS Sintered glass filters:
Used for air filtration, made of finely ground glass
Glass filter

21. FILTERS Membrane filters: Cellulose nitrate - Also called gradacol MEM
- To separate viruses, to know their size
Cellulose acetate or millipore filters or oxoid MEM filters
HEPA: High efficacy particulate air filters
Membrane filter

22. RADIATION
Non-ionising radiation - Infrared and ultraviolet rays - low energy type
- Control of closed environment with UV lamp
- Bacteriological laboratory, inoculation hoods, laminar flow

23. RADIATION
Ionising radiation - Gamma rays, X rays and cosmic rays lethal to penetrative power
No appreciable increase in temperature – ‘cold sterilisation’
Use: Sterilising pharmaceuticals, medical, dental equipment, sterilising plastics, syringes, swabs, catheters, oil grease

24. CHEMICAL METHODS
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25. CHEMICAL METHODS Alcohols Protein denaturation and lipid dissolution
Bactericidal, fungicidal
Not effective on spores and viruses
Commonly used - Ethyl alcohol, isopropyl alcohol
Concentration 60-90% in water

26. CHEMICAL METHODS Aldehydes
Active against amino group in protein molecule
Formaldehyde
Used for sterilising instruments, heat-sensitive catheters, fumigation of wards, sick rooms and laboratories
Glutaraldehyde
Disinfection of medical equipment like cystoscopes and bronchoscope
Effective against tubercle bacilli, fungi and viruses

27. DYES Aniline dyes Brilliant green, malachite green and crystal violet
Non-toxic, non-irritant
Active against Gram-positive organisms
Used as selective agents in culture media
Acridine dyes
Proflavine, acriflavine and euflavine
Impair DNA, destroy the reproductive capacity of the cell

28. CHEMICAL METHODS Phenols Lister - antiseptic surgery
Distillation of tar between 170°C and 270°C
Damage to cell membrane, release cell contents and cell lysis
Cresols, chlorhexidine, hexachloraphane
Disinfection of floors, excreta, preoperative disinfection of skin

29. CHEMICAL METHODS Halogens Iodine – Skin disinfectant
Bactericidal, sporicidal
Iodophores more active
Chlorine – Used as hypochlorite
Bactericidal
Disinfect water supplies, swimming pools and used in diary industries

30. GASES
Ethylene oxide - Kills microorganisms by altering their DNA by alkylation of amino carboxyl, hydroxyl and sulphydryl groups in protein molecules - Used in sterilising packaged heat-sensitive devices - Respirators, heart–lung machines, dental equipment, sutures, books and clothing

31. GASES Formaldehyde Fumigation of theatres and rooms
150 g of KMnO4 to 280 ml formalin for every 1000 cu ft.
Doors sealed, opened after 48 hrs
Betapropiolactone (BPL)
Condensation product of ketane and formaldehyde
Hydrogen peroxide fogging
Short cycle time, non-toxic

32. SURFACE ACTIVE AGENTS
Act by altering energy relationship at interfaces - reduction in surface tension
Classification
Anionic, cationic, amphoteric, non-ionic
Antibacterial, fungicidal, virucidal
Cetavlon, cetrimide

33. SALTS OF HEAVY METALS Copper, silver, mercury
Combine with sulphydryl groups of cell enzymes, denaturation of enzymes
Highly toxic
Thiomersal, mercurochrome less toxic, used as mild antiseptics
Copper salts - fungicide

34. PLASMA
Produced at very high temperature or low temperature in strong electromagnetic fields
Plasma consists of ions, electrons and free radicals
Used for arthroscopes, urethroscopes

35. DISINFECTION Spaulding Classification
Eagle H Spaulding believed that the method used to disinfect an object will depend on the object’s intended use

36. WHICH PROCEDURE TO USE? Procedure Items in each category Category
High level disinfection
Items that: (1) enter the tissue; (2) Enter vascular system; (3) through which blood flows
Critical
Intermediate
level disinfection
Items that: (1) touch mucous membranes; (2) touch non-intact skin (e.g. endoscopes, respiratory therapy equipment, thermometer)
Semi-critical
Low level disinfection
Items such as bedpans, blood pressure cuffs, and bedside tables
Non-critical