2. Sterilization
It is defined as the process by which an article, surface / medium is
freed of all living microroganisms either in vegetative or spore
state.
Antiseptic :
Prevention of infection by inhibiting the growth of bacteria in
wounds or tissues.
Bacteriostatic Agents:
Agents that inhibit bacterial growth
Bacteriocidal Agents:
Agents that kill the bacteria
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3. Germicide: An agent that kills certain microorganisms.
Bactericide: An agent that kills bacteria. Most do not
kill endospores.
Viricide: An agent that inactivates viruses.
Fungicide: An agent that kills fungi.
Sporicide: An agent that kills bacterial endospores of
fungal spores.
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4. • Physical methods
• Chemical methods
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1) Sunlight
2) Drying
3) Dry heat: Flaming, Incineration, Red heat, Hot air oven
4) Moist heat: Vaccine Bath, Inspissation, Pasteurization,
steam under normal pressure,
steam under pressure(Autoclave)
5) Filtration: Candles, Asbestos, Membranes, Syringe, Sintered
6) Radiation
7) Ultrasonic and sonic vibration
F I R H
V I P
C A M S 2
5. SUNLIGHT
It has bactericidal activity and plays an important role in
spontaneous sterilization that occurs under natural
conditions.
Action is due to its content of ultraviolet rays
Has an active germicidal effect due to the combined
effect of ultraviolet and heat rays.
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6. DRYING
Moisture is essential for bacteria
Drying therefore has a deleterious effect on most bacteria
Viruses and spores are unaffected by drying
So drying is a very unreliable method.
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7. HEAT
It is the most popular, reliable and widely used method of sterilization
Two methods - Dry heat
Flaming Incineration
Red Heat Hot Air Oven
- Moist heat
Temp below 100o C Temp at 100o C
Steam at normal pressure Steam under pressure
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8. • Most reliable method
Factors influencing the sterilization by heat:
1) Nature of heat – dry/moist
2) Temperature & time
3) Number of microorganisms present
4) Characteristics of organisms
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9. Dry heat -
Oxidative damage to cell constituents
Protein denaturation
Increased electrolyte levels
Moist heat-
• Denaturation & coagulation of protein
• Protein hydrolysis & breakdown
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10. FLAMING
A simple & effective
method
Loops or wires ,glass slides,
cover slips the tips of the
instruments are held in a
Bunsen flame without
making red-hot. These
materials may be dipped in
a disinfectant before
flaming
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11. Temperature : 870-980 0C
INCINERATION
This is an excellent method for safely destroying
materials such as contaminated cloth, animal carcasses
and pathologic materials
Plastics such as PVC and polythene can be dealt with
similarly
Polystyrene materials emit clouds of dense black smoke
and hence should be autoclaved in appropriate containers.
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13. HOT AIR OVEN
•
•
•
This is the most widely used method of sterilization by
dry heat.
This type of energy does not penetrate materials easily
and thus, long periods of exposure to high temperatures
are necessary.
A holding period of 160oC( 320oF) for 1 hr
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14. •
•
Since hot air is a bad conductor of heat its penetrating
power is low.
The oven is usually heated by electricity.
•
•
It must be fitted with a fan to ensure even distribution of
air and elimination of air pockets.
The material should be arranged so as to allow free
circulation of air in between the objects. 14
15. Glassware should be perfectly dry before being placed in
the oven.
The oven must be allowed to cool slowly before the
door is opened, since the glassware may crack due to
sudden or uneven cooling.
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Temperature(oC) Holding Time
140 3 Hrs
160 1 Hr
180 30minutes
17. ADVANTAGES
•Effective and safe sterilization of metal instruments and
mirrors
•No corrosion of Carbon steel instruments and burs
DISADVANTAGES
•Long cycles
•Poor penetration
•Uneven heating
•Damage to heat sensitive items
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18. 18
• Physical methods:
• By recording the temperature -
Thermometers
Thermocouples
• Chemical method:
• Browne’s tube- induces colour change
• Biological tests:
• Paper strips impregnated -106 spores
non-toxigenic strains of Clostridium tetani
19. • Avoid fabrics, rubber articles ,gloves etc
• Glass ware must be perfectly dry,
• Wrap in kraft paper.
• Avoid - Overloading,
• Ensure uniform circulation.
• Cool & open.
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20. Mechanism of action:
• Denaturation of enzymes & proteins
• Coagulation of cytoplasm
Types:
• Moist heat below 100oC
• Moist heat at 100oC ( with/ without pressure)
• Moist heat above 1000C
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Moist heat sterilization
21. Moist heat below 100ᵒc
Vaccine bath - 60O C – 1 hour
- serum & body fluids
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22. • water jacketed copper box.
• temperature 75° to 80°C (thermostat).
• Inspissator used
Uses:
• sterilization of egg media/ serum media
• heat labile sugar media.
Eg:
• Lowenstein- Jensen medium( LJ),
• Loeffler’s serum slope etc.
Inspissation
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23. Principle:
is based on fractional sterilization procedure.
First heating (Day 1- 1½ hours)
destroys the vegetative forms of the bacteria.
second heating (2nd day -1 hour)
the spores are allowed to germinate
the germinated forms are destroyed.
The third - consecutive heating (3rd day - 30 minutes)
ensures complete sterilization
without destroying constituents of the media.
Inspissator
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25. Steam sterilizer (Koch/Arnold):
Tyndallization:
• It is intermittent sterilization method
• Sugar media, gelatin ,milk get damaged at
higher temperatures.
• At 100 o C - 30 minutes for three
successive days.
Boiling
Moist heat at 100oc
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26. Boiling
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Vegetative bacteria are killed almost immediately at
90-1000C, but sporing bacteria require prolonged
periods of boiling.
Boiling water is not considered as a sterilizing agent
because destruction of bacterial spores and
inactivation of viruses cannot always be assured. It
is considered as a method for disinfection
27. Autoclave
It is a high pressure sterilizer
Designed by Chamberland -1880
Working Conditions: 1210C, 15lbs/sq inch 15minutes
Other conditions: 1260C, 20lbs/sq inch, 10minutes,
1330C, 30lbs/sq inch, 3minutes
Principle :
When water is boiled within a closed vessel at increased pressures,
the boiling point of water will rise above 100o C.
The increase in pressure yields an increase in effective temperature
Moist heat above 100oc
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31. • Liquids such as sera , heat labile substances,
• sugars & urea used for media preparation.
• Separation of bacterial toxins from bacteria
• Isolation of organisms (scanty in fluids).
• Viruses are too small (cannot be filtered )
Filtration
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