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Disinfection
and
Sterilization
Disinfection
It is the Killing of most microbial forms. Some
resistant forms of organisms e.g. bacterial spores,
mycobacterium , viruses, fungi may remain viable.
Disinfection can achieved by boiling, pasteurization
,UV rays and chemical agents.
Antisepsis (by antiseptics)
Inhibition or elimination of microbial
forms on the skin or living tissue.
We can use chemical agents like ethyl
alcohol.
It is not suitable for systemic
administration.
Germicides
Germicides are chemical agents.
They are used for Killing of microbial
forms but spores may remain viable.
Sporicide
It is Germicide able to killing bacterial
spores.
Cleaning
It is the removal of visible dust, dirt and
foreign material by water and soap.
It usually precede disinfection and
sterilization .
Decontamination
It is a general term applied to any
procedure by which microorganism are
reduced to a level where the equipments is
safe for handling.
sterilization
Sterilization is the Killing of all living forms of
microbes (bacteria, fungi and viruses)
Mthods of sterilization
I-Heat sterilization (moist or dry)
II-Low temperature sterilization
III- sterilization by radiation
IV- sterilization by Filtration
I-Heat Sterilization
Is the most practical
efficient and inexpensive
method of sterilization, it
can be used in two forms:
moist heat and dry heat
A: Moist heat
Is much more efficient
than dry heat, because it
kills the microbes by
coagulation and denaturing
of their enzymes and
structural protein.
a-Moist heat at a temperature below
100oC
An example is pasteurization of milk by heat at
either 63oC for 30min or at 72oC for 20sec and
immediately cooling to below 10oC.
Pasteurization can destroy all non- spore forming
pathogens.
b- Moist heat at a temperature of
100oC (boiling)
Boiling at 100oC for 20Min. to kill all vegetative
bacteria and hepatitis B virus but not all bacterial
spore . This method may be used for disinfection
of surgical equipment).
c- Moist heat at a temperature above 100oC
(autoclave)
• The sterilizing agent is saturated
• water steam under high pressure.
• Equipment used called: Autoclave
• Saturated steam should be free
from air.
• At 2bar (atmospheric pressureX2), the temperature
is 121oC and strilization time is 20-30 min
• At 3bar the temperature is 134oC and sterilization
time 3-6min
• The autoclave is used for sterilization of
culture media, surgical instruments, dressings,
gowns, cotton, gauze.
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Advantages of moist heat
1-Steam has high penetrating power.
2--Not toxic
3-Low cost and not time consuming.
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Disadvantage of moist heat
1- Some items can not withstand the high
temperature of steam
2- Not suitable for powder and oils.
B-Dry Heat
• It is kill the microorganisms by destructive
oxidation of essential cell constituents
• it is less efficient than moist heat.
• Methods of dry heat
1-Incineration
used for tratment of dead animals, infectious
hospital wastes, surgical dressings, needles.
2-Red heat
Exposing wires, loops, points of
forceps to flame until become red.
3-Hot air oven
Oven is an double walled metal chamber heated by
electricity, to a constant temperature
Sterilization time
and temperature:
2 hr 160oC for 2Hr
One hr 170oC.
30 Min at 180oC
Hot air oven is used for sterilization of:
glassware, ointments, powders, oils, and metallic
instruments
II-Low temperature sterilization
1- By Gas
Ethylene oxide 450-1200 mg/L at 56oC
Time of exposure varies from 3-6 hours.
Its Advantage is capability of sterilizing the instruments
that cannot be subjected to steam or hot air oven
without any damage .
Disadvantage is :long duration ,High cost and toxicity.
2-By liquids
1-PERACETIC ACID 0.2%
2-GLUTARALDEHYDE (Cidex)
2%
III-Sterilization by Radiation
1-Gamma rays
2- β-rays (High- energy electrons)
These are used for sterilization of Heat
sensitive items like:
Prepacked disposable plastic items like plastic syringe
,catheters ,gloves, surgical suture, IV sets and plastic
Petri dishes.
• 3-Ultra Violet light
• It is present in sun rays
• It is produced artificially by
mercury lamps
• It has weak penetrating power
• It is used to reduce the number of bacteria in air
and for surface disinfection in certain area e.g.
operation room , lab safety cabinet.
IV-Sterilization by Filtration
•This is the a mechanical
exclusion of microorganisms
from biological fluids which are
sensitive to heat as serum,
plasma, hormones, vitamins.
• Filters used have pore size of
less than 0.45um.
•Viruses and bacteria as
mycoplasma pass through
filters