Microbiology
With Diseases by Taxonomy PowerPoint® Lecture Slides
Second Edition
Industrial
Biotechnology
Module 3
Sterilization and Kinetics
PART A
Lecture 10 –Medium
Sterilization methods
Dr. Vijayalakshmi Shankar
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Sterilization
Sterilization
The term sterilization, means destruction of all living
organisms and their spores or their complete removal from
the preparation.
Methods Five general methods are used to sterilize pharmaceutical
products:
of 1. Steam
2. Dry heat
Sterilizati 3. Filtration
on 4. Gas
5. Ionizing radiation
Disinfection by Chemicals
The method is determined largely by the nature of the
preparation and its ingredients.
Sterilization
Steam sterilization is conducted in an autoclave and
employs steam under pressure.
It is usually the method of choice if the product can
Steam withstand it
The temperature required for dry heat sterilization is about
Sterilizati 150°C to 170°C or 302°F to 338°F.
on When moisture is present, bacteria are coagulated and
destroyed at a considerably lower temperature than when
moisture is absent.
In fact, bacterial cells with a large percentage of water are
generally killed rather easily.
Spores, which contain a relatively low percentage of
water, are comparatively difficult to destroy.
The mechanism of microbial destruction in moist heat is
thought to be by denaturation and coagulation of some of
the organism’s essential protein.
Steam Death by dry heat is thought to be by dehydration of the
microbial cell followed by slow oxidation.
Sterilizati Because it is not possible to raise the temperature of steam
on above 100°C (212°F) under atmospheric conditions,
pressure is employed to achieve higher temperatures.
It is the temperature, not the pressure, that destroys the
microorganisms, and the application of pressure is solely to
increase the temperature of the system.
Steam sterilization is conducted in an autoclave and
employs steam under pressure.
Industrial
autoclave
MOIST HEAT
Sterilization By
Moist heat
Moist heat at Moist heat Moist heat
Below 100˚C At 100˚C At above 100˚C
Boiling
e.g.. Autoclave
Tyndallization
pasteurization
11
Sterilization
Sterilization
Pasteurizati
on
Dry heat sterilization is usually carried out in ovens
designed for this purpose.
The ovens may be heated either by gas or electricity and are
Dry Heat generally thermostatically controlled.
Sterilizati Because dry heat is less effective in killing microorganisms than
is moist heat, higher temperatures and longer periods of
on exposure are required.
These must be determined for each product with
consideration to the size and type of product and the
container and its heat distribution characteristics.
Dry heat sterilization is usually conducted at 150°C to 170°C
for not <2 hours.
Dry heat is also an effective method for sterilizing glassware
and surgical instruments.
Sterilization
Sterilization
Sterilization
Sterilization
Sterilization
Sterilization
Sterilization by filtration, which depends on the physical
Sterilizati removal of microorganisms by adsorption on the filter
medium or by a sieving mechanism, is used for heat-
on by sensitive solutions.
Filtration Commercially available filters are produced with a variety of
pore size specifications.
It would be well to mention briefly one type of modern
filter, the Millipore filter.
The Millipore filter is a thin plastic membrane of cellulosic
esters with millions of pores per square inch.
The major advantages of bacterial filtration
Sterilizati • its speed in the filtration of small quantities of solution,
include
• its ability to sterilize thermolabile materials,
on by • the relatively inexpensive equipment required,
• the development and proliferation of membrane filter
Filtration technology,
• and the complete removal of living and dead
Onemicroorganisms
disadvantageand otherbecause
is that particulate
thematter from thetends to
membrane
besolution.
fragile, it is essential to determine that the assembly was
properly made and that the membrane was not ruptured or
flawed during assembly, sterilization or use.
Also, filtration of large volumes of liquids requires
more time, particularly if the liquid is viscous.
Filtration does not kill microbes, it separates them
out.
Membrane filters with pore sizes between 0.22-
0.45 μm are commonly used to remove particles
from solutions that can't be autoclaved.
It is used to remove microbes from heat labile
liquids such as serum, antibiotic solutions, sugar
solutions, urea solution.
Sterilization
Some heat-sensitive and moisture-sensitive materials can be
Gas sterilized much better by exposure to ethylene oxide or
propylene oxide gas than by other means.
Sterilizati These gases are highly flammable when mixed with air but can
on be employed safely when properly diluted with an inert gas
such as carbon dioxide or a suitable fluorinated hydrocarbon.
Sterilization by this process requires specialized equipment
resembling an autoclave, and many combination steam
autoclaves and ethylene oxide sterilizers are commercially
available.
Greater precautions are required for this method of
sterilization than for some of the others, because the variables
—for instance, time, temperature, gas concentration, and
humidity—are not as firmly quantitated as those of dry heat and
steam sterilization.
Sterilizati Techniques are available for sterilization of some types of
pharmaceuticals by gamma rays and by cathode rays, but
on by application of such techniques is limited because of the highly
specialized equipment required and the effects of irradiation
Ionizing on the products and their containers.
Radiation The exact mechanism by which irradiation sterilizes a media
preparation is still subject to investigation.
One of the proposed theories is alteration of the chemicals
within or supporting the microorganism to form deleterious
new chemicals capable of destroying the cell.
Another theory proposes that vital structures of the cell,
such as the chromosomal nucleoprotein, are disoriented or
destroyed.
It is probably a combination of irradiation effects that causes
the cellular destruction, which is complete and irreversible.
Sterilization
Sterilization
CHEMICAL METHODS OF DISINFECTION:
Disinfectants are those chemicals that destroy
pathogenic bacteria from inanimate surfaces. Some
chemical have very narrow spectrum of activity and
some have very wide.
ALCOHOLS:
Examples: Ethyl alcohol, isopropyl alcohol and methyl
alcohol
Application: A 70% aqueous solution is more effective
at killing microbes than absolute alcohols. 70% ethyl
alcohol (spirit) is used as antiseptic on skin.
Disadvantages: Skin irritant, volatile (evaporates
rapidly), inflammable
