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Disinfection and sterilization
Sterilization is the killing or removal of all microorganisms, including bacterial spores which are highly
resistant. Sterilization is an absolute term, i.e. the article must be sterile meaning the absence of all
microorganisms.
Disinfection is the killing of many, but not all microorganisms. It is a process of reduction of number of
contaminating organisms to a level that cannot cause infection, i.e. pathogens must be killed. Some
organisms and bacterial spores may survive.
Disinfection and sterilization are both decontamination processes. While disinfection is the process of
eliminating or reducing harmful microorganisms from inanimate objects and surfaces, sterilization is the
process of killing all microorganisms. That is the main difference between sterilizing and disinfecting.
Sterilization also destroys the spores of various organisms present on surfaces, in liquids, in medication,
or in compounds such as biological culture media. Such "extreme" forms of decontamination are needed
during critical times like surgery, or in environments like industrial, laboratory or hospital. It is more
practical to use disinfection in everyday life.
Comparison chart
Definition
Methods
Disinfect
Sterilize
To disinfect means to eliminate most
To sterilize means to kill ALL
harmful microorganisms (not including
microbes - whether harmful or
their spores) from surfaces or objects;
not - and their spores present on a
inactivate viruses.
surface or object.
Phenolic disinfectants, heavy metals,
Heat, chemicals, irradiation, high
halogens (eg chlorine), bleach, alcohols,
pressure, and filtration.
hydrogen peroxide, detergents, heating
and pasteurization.
Types
Air disinfectants, alcohols, aldehydes,
Steam, heating, chemical
oxidizing agents, phenolics.
sterilization, radiation
sterilization, sterile filtration.
Application
Disinfect
Sterilize
Disinfection is used mostly to
Sterilization is used for food,
decontaminate surfaces and air.
medicine and surgical
instruments.
Disinfectants are chemicals that are used for disinfection. Disinfectants should be used only on inanimate
objects.
Antiseptics are mild forms of disinfectants that are used externally on living tissues to kill
microorganisms, e.g. on the surface of skin and mucous membranes.
Methods of Sterilization and Disinfection
Sterilization can be done by three methods: physical, chemical and physiochemical. Physical method
includes heat, radiation, and filtration. Chemical methods involve using liquid and gaseous chemicals.
Physiochemical is a combination of physical and chemical method.
Uses of Sterilization
1. Sterilization for Surgical Procedures: Gloves, aprons, surgical instruments, syringes etc. are to be
sterilized.
2. Sterilization in Microbiological works like preparation of culture media, reagents and equipment
where a sterile condition is to be maintained.
Disinfection is usually carried out by using disinfectants (chemicals). Some disinfectants may be very
effective and have a wide spectrum (have the capability of destroying a wide variety of microorganism)
while others may have a narrow spectrum but, they may be easy to use, be non-toxic or inexpensive.
CLASSIFICATION OF METHODS
Sterilization and disinfection are done by :
(A). Physical Agents
1. Heat
2. Radiation
3. Filtration
(B). Chemical Agents
In practice, certain methods are placed under sterilization which in fact do not fulfill the definition of
sterilization such as boiling for 1/2 hr and pasteurization which will not kill spores.
Sterilization

Steam - Used in machines called autoclaves. Autoclaving is one of the most common methods
of sterilization. Principle: In this method sterilization is done by steam under pressure. Steaming
at temperature higher than 100°C is used in autoclaving. The temperature of boiling depends on
the surrounding atmospheric pressure. A higher temperature of steaming is obtained by
employing a higher pressure. When the autoclave is closed and made air-tight, and water starts
boiling, the inside pressures increases and now the water boils above 100°C. At 15 ib per sq.
inch pressure, 121°C temperatures is obtained. This is kept for 15 minutes for sterilization to kill
spores. It works like a pressure cooker.

Autoclaves use steam heated to 121–134 °C (250–273 °F). To achieve sterility, a holding time
of at least 15 minutes at 121 °C (250 °F) or 3 minutes at 134 °C (273 °F) is required. Autoclave
treatment inactivates all fungi, bacteria, viruses and also bacterial spores. Pressure cooking food
is also steam sterilization though it is not that thorough.

Autoclave is a metallic cylindrical vessel. On the lid, there are: (1) A gauge for indicating the
pressure, (2) A safety valve, which can be set to blow off at any desired pressure, and (3) A
stopcock to release the pressure. It is provided with a perforated diaphragm. Water is placed
below the diaphragm and heated from below by electricity, gas or stove. Working of Autoclave.
(a) Place materials inside, (b) Close the lid. Leave stopcock open, (c) Set the safety valve at the
desired pressure, (d) Heat the autoclave. Air is forced out and eventually steam ensures out
through the tap, (e) close the tap. The inside pressure now rises until it reaches the set level (i.e.
15 Win), when the safety valve opens and the excess steam escapes, (f) Keep it for 15 minutes
(holding time), (g) Stop heating, (h) Cool the autoclave below 100°C, (i) Open the stopcock
slowly to allow air to enter the autoclave.

Heating – Under heating flaming, incineration, boiling in water, tyndalization, dry heat. These
methods inactivate and kill microorganisms in objects like glass, metals. Boiling in water for 15min
inactivates viruses and kills most vegetative bacteria. However it has no effect on the spores.
Tyndilization means boiling for 20 minutes and then cooling, again re-boiling and cooling for three
times. This method is more effective on sporulating bacteria than just boiling. Dry heat method can
be used on powders and items that bear very high them of heat.

Hot Air Oven (Sterilizer). It Is one of the most common method used for sterilization. Glass
wares, swab sticks, all-glass syringes, powder and oily substances are sterilized in hot air oven.
For sterilization, a temperature of 160°C is maintained (holding) for one hour. Spores are killed
at this temperature. It leads to sterilization.

Hot Air Oven is an apparatus with double metallic walls and a door. There is an air space
between these walls. The apparatus is heated by electricity or gas at the bottom. On heating, the
air at the bottom becomes hot and passes between the two walls from below upwards, and then
passes in the inner chamber through the holes on top of the apparatus. A thermostat is fitted to
maintain a constant temperature of 160°C.

Chemical sterilization – Chemicals like Ethylene oxide, Bleach, Glutaraldehyde and Formaldehyde,
Phthalaldehyde, Hydrogen Peroxide, Dry sterilization process, Peracetic acid and Silver are used in
varying degrees. Products that can get damaged due to heat are subjected to chemical sterilization for
+e.g. biological materials, fiber optics, electronics, and plastics. Ethylene oxide gas and Ozone gas
oxidize most organic matter. Though bleach and Glutaraldehyde and formaldehyde solutions is used
as a disinfectant, it’s a much more concentrated in sterilization also infected item is left immersed for
long duration for effective sterilization. Dry sterilization process with chemicals is useful for
sterilizing plastic bottles medical and pharmaceutical applications.

Radiation sterilization - Electron beams, X-rays, gamma rays, or subatomic particles are used for
sterilizing disposable medical equipment, such as syringes, needles, cannulas, IV sets and biological
safety cabinets between uses.

Sterile filtration - Clear liquids that would be damaged by heat, irradiation or chemical sterilization
can be sterilized by mechanical filtration. Filtration is done through pores that are smaller in size than
the organism in question and this has to be done very slowly.
Types Disinfection

Air disinfectants - disinfectant is dispersed as either as an aerosol or vapour at a sufficient
concentration in the air to cause the number of viable infectious microorganisms to be significantly
reduced. Chemicals used propylene glycol and triethylene glycol.

Alcohols - high-concentration can effectively inactivate viruses such as HIV, hepatitis B, and
hepatitis C. Chemicals present usually ethanol or isopropanol. It is safe and inexpensive to use in
household environment, care has to be taken around inflammable items.

Oxidizing agents – Cause the microorganism to collapse. Chlorine and oxygen are strong oxidizers,
so their compounds are used for e.g. common household bleach. In fact it is the most cost-effective
home disinfectant (sodium hypochlorite solution) is used to clean toilets, drains, surfaces, swimming
pool.

Phenolics – It is oldest known disinfectant for e.g. mouthwashes, Dettol. Chemicals - Phenol,
Chloroxylenol