sterilization and methods of sterilization

WHAT IS STERILIZATION:
Sterilization can be defined as any process that
effectively kills or eliminates transmissible agents
(such as fungi, bacteria, viruses and prions) from a
surface, equipment, foods, medications, or
biological culture medium.

METHODS OF STERILIZATION
 The various methods of sterilization are:
 1. Physical Method
a. Thermal (Heat) methods
b. Radiation method
c. Filtration method
 2. Chemical Method
a. Gaseous method

PHYSICAL METHODS:
1. HEAT STERILIZATION:
 Heat sterilization is the most widely used and
reliable method of sterilization, involving
destruction of enzymes and other essential cell
constituents.
 This method of sterilization can be applied only to
the THERMO STABLE PRODUCTS, but it can be
used for MOISTURE-SENSITIVE MATERIALS.
i) Dry Heat (160-1800˚C) Sterilization for
thermo stable products
ii) moist heat (121-1340 ˚C) sterilization is
used for moisture- resistant materials.

 The efficiency with which heat is able to
inactivate microorganisms is dependent upon
i) the degree of heat, the exposure time and
ii) the presence of water.
 The action of heat will be due to induction of
lethal chemical events mediated through the
action of water and oxygen.
 In the presence of water much lower
temperature time exposures are required to kill
microbe than in the absence of water.

THERMAL (HEAT) METHODS
Thermal methods includes:
i) Dry Heat Sterilization
Ex:1. Incineration
2. Red heat
3. Flaming
4. Hot air oven
ii) Moist Heat Sterilization
1.Dry saturated steam – Autoclaving
2. Boiling water/ steam at
atmospheric
pressure
3. Hot water below boiling point

Dry Heat Sterilization
 It employs higher temperatures in the range of
160-180˚C and requires exposures time up to
2 hours, depending upon the temperature
employed.
 The benefit of dry heat includes good
penetrability and non-corrosive nature which
makes it applicable for sterilizing glass wares
and metal surgical instruments. It is also used
for sterilizing non-aqueous thermo stable
liquids and thermo stable powders.

 Dry heat destroys bacterial endotoxins (or
pyrogens) which are difficult to eliminate by
other means and this property makes it
applicable for sterilizing glass bottles which
are to be filled aseptically

Moist Heat Sterilization
 Moist heat sterilization involves the use of
steam in the range of 121-134˚C. Steam under
pressure is used to generate high temperature
needed for sterilization. Saturated steam acts
as an effective sterilizing agent.

Autoclave
 Autoclaves use pressurized steam to destroy
microorganisms, and are the most dependable
systems available for the decontamination of
laboratory waste and the sterilization of
laboratory glassware, media, and reagents.
For efficient heat transfer, steam must flush
the air out of the autoclave chamber.
 Generally the conditions employed are
Temperature upto121-134˚C for 15-20 min under
15 lbs pressure,based on type of metiral used.

Radiation Sterilization
 Many types of radiation are used for
sterilization like electromagnetic radiation (e.g.
gamma rays and UV light), particulate
radiation (e.g. accelerated electrons).The
major target for these radiation is microbial
DNA.
 Radiation sterilization with high energy gamma
rays or accelerated electrons has proven to be
a useful method for the industrial sterilization
of heat sensitive products.

 Radiation sterilization is generally applied to
articles in the dry state; including surgical
instruments, sutures, prostheses, unit dose
ointments, plastic syringes and dry
pharmaceutical products.
 UV light, with its much lower energy, and poor
penetrability finds uses in the sterilization of
air, for surface sterilization of aseptic work
areas, for treatment of manufacturing grade
water, but is not suitable for sterilization of
pharmaceutical dosage forms.

Filtration Sterilization
 Filtration process does not destroy but
removes the microorganisms. It is used for
both the clarification and sterilization of liquids
and gases as it is capable of preventing the
passage of both viable and non viable
particles.
 The major mechanisms of filtration are
sieving, adsorption and trapping within the
matrix of the filter material.
 Ex:HEPA FILTERS

 Sterilizing grade filters are used in the
treatment of heat sensitive injections and
ophthalmic solutions, biological products and
air and other gases for supply to aseptic areas.
They are also used in industry as part of the
venting systems on
fermentors, centrifuges, autoclaves and freeze
driers. Membrane filters are used for sterility
testing

 There are two types of filters used in filtration
sterilization:
(a) Depth filters:
(b) Membrane filters: These are porous
membrane about 0.1 mm thick, made of
cellulose acetate, cellulose
nitrate, polycarbonate, and polyvinylidene
fluoride, or some other synthetic material.

CHEMICAL STERILIZATION
METHOD
GASEOUS METHOD
 The chemically reactive gases such as
formaldehyde, (methanol, H.CHO) and
ethylene oxide (CH2)2O possess biocidal
activity. Ethylene oxide is a colorless,
odorless, and flammable gas.
 The mechanism of antimicrobial action of the
two gases is assumed to be through
alkylations of sulphydryl, amino, hydroxyl and
carboxyl groups on proteins and amino groups
of nucleic acids.

 The concentration ranges (weight of gas per
unit chamber volume) are usually in range of
800- 1200 mg/L for ethylene oxide and 15-100
mg/L for formaldehyde with operating
temperatures of 45-63°C and 70-75°C
respectively.
 Both of these gases being alkylating agents
are potentially mutagenic and carcinogenic.
They also produce acute toxicity including
irritation of the skin, conjunctiva and nasal
mucosa

MERITS, DEMERITS AND
APPLICATIONS OF
DIFFERENT METHODS OF
STERILIZATION

S.no METHOD
MECHANISM
MERITS DEMERITS APPLICATIONS
1 Heat
sterilization
Destroys
bacterial
endo toxins
Most widely
used and
reliable
method of
sterilization,
involving
destruction of
enzymes and
other essential
cell
constituents
Can be
applied only
to the
thermo
stable
products
Dry heat is applicable
for sterilizing glass
wares and metal
surgical instruments
and moist heat is
the most dependable
method for
decontamination of
laboratory waste and
the sterilization of
laboratory glassware,
media, and reagents.

S.no METHOD
MECHANISM
1
2
Gaseous
sterilization
Radiation
sterilization
Alkylation
Ionization of
nucleic acids
Penetrating
ability of gases.
It is a useful
method for the
industrial
sterilization of
heat sensitive
products
Gases being
alkylating agents
are potentially
mutagenic and
carcinogenic.
Undesirable
changes occur in
irradiated
products,an
example is
aqueous solution
where radiolysis
of water occurs.
Ethylene oxide gas has
been used widely to
process heat-sensitive
devices.
Radiation sterilization is
generally applied to articles
in the dry state; including
surgical instruments,
sutures, prostheses, unit
dose ointments, plastics

S.n
o
METHOD
MECHANISM
1 Filtration
sterilization
Does not destroy
but removes the
microorganisms
It is used for both
the clarification and
sterilization of
liquids and gases as
it is capable of
preventing the
passage of both
viable and non
viable particles
Does not
differentiate
between viable
and non viable
particles
This method is Sterilizing
grade filters are used in
the treatment of heat
sensitive injections and
ophthalmic solutions,
biological products and
air and other gases for
supply to aseptic areas

Pharmaceutical Importance of
Sterilization
 • Moist heat sterilization is the most efficient biocidal
agent. In the pharmaceutical industry it is used for:
Surgical dressings, Sheets, Surgical and diagnostic
equipment, Containers, Closures, Aqueous injections,
Ophthalmic preparations and Irrigation fluids etc.
 • Dry heat sterilization can only be used for thermo
stable, moisture sensitive or moisture impermeable
pharmaceutical and medicinal. These include products
like; Dry powdered drugs, Suspensions of drug in non
aqueous solvents, Oils, fats waxes, soft hard paraffin
silicone, Oily injections, implants, ophthalmic
ointments and ointment bases etc.


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