Sterilization and sterilization methods – Pharmaceutical Microbiology Third Semester PDF Notes

Concept of sterilization and sterilization methods


• Origin of sterilization concepts

• Definition of sterilization, disinfection, antisepsis,
degerming and sanitization


At the end of this lecture, the student will be able to:

• Explain different terminologies related to sterilization

• Explain ‘D value’ and ‘Z value’

• List the different methods of sterilization

History of

• In ancient times, demons and evil spirits were thought to
be the cause of pestilence and infection.

• Methods involving witchcraft and magic were used to drive
them away.

• 3,000 BC – The use of antiseptics such as pitch or tar,
resins and aromatics was widely employed by the Egyptians in embalming bodies-
known as Mummies.

Moses  (circa  1450 
BC)  was  the 
first  to  prescribe 
a  system  of purification by fire

• Greek Infantry men known as hoplite sometimes fought
naked, especially against fast-moving cavalry they believed that pieces of
clothing carried into a wound by a penetrating sword or spear point were more
likely to cause infection.

Galen (130-200 AD),
a Greek who practiced medicine in Rome and was the most distinguished physician
after Hippocrates, boiled instruments used in caring for wounded Roman

• In Hippocrates of
(460-377 BC), was the first to separate medicine from philosophy and
disproved the idea that disease was punishment for sin. He also advocated
irrigation of wounds with wine or boiled water, as an aseptic method

Denis Papin, a
French physicist, invents the “Digester” (pressure cooker) in 1680

• In 1758 – the earliest use of surgical glove. Dr. Johann Julius Walbaum formed a
glove from the intestines of a sheep and used it to deliver babies.

Ignaz Semmelweis,
an Hungarian obstetrician, advocated in 1847 the value of handwashing and
fingernail scrubbing.

• In 1862, French chemist and microbiologist Louis Pasteur publishes his findings on
how germs cause disease, which he later uses to develop the pasteurization

• Joseph Lister,
an English physician, reduced the mortality rate of his patients in 1867 by
using a carbolic solution spray as he operated, he then used it in the wound,
on the articles in contact with the wound and on the hands of the operating

• In 1885, Ernst von
, a German physician, first used the steam sterilizer for the
sterilization of surgical dressings.

• Gustav Neuber introduced mercury chloride in 1886 to clean
his apron

• He   advocated   scrubbing  
the furniture with disinfectant and sterilizing everything in contact
with the wounds.

• Around 1889, Dr.
William Stuart Halstead
, to remedy a nurse’s complaints of dermatitis
caused by the strong chemical disinfectants used to perform hand scrubs, asked
the Goodyear Rubber Company   if   they  
could   create   a  
thin rubber glove to protect their hands.

Terminology of Microbial Control

  Sterilization  refers 
to  any  process 
that  involves  the 
removal  or destruction of all
forms of microbial life

• A sterilizing agent is called a sterilant

• Sterile means “Free from viable micro-organisms”

Disinfection describes a process that eliminates many or
all pathogenic microorganisms, except bacterial spores, on inanimate objects

Antisepsis is the prevention of infection or sepsis and is
accomplished with antiseptics.

Degerming is the mechanical removal, rather than the
killing, of most of the microbes in a limited area.

Sanitization is intended to lower microbial counts to safe
public health levels and minimize the chances of disease transmission from one
user to another

Terminology Relating
to the Control of Microbial Growth

The Rate of
Microbial Death

When bacterial populations are heated or treated with
antimicrobial chemicals, they usually die at a constant rate.

Microbial Exponential
Death Rate
: An Example

The rate and pattern
of microbial death

If the death curve is plotted logarithmically, the death
rate is constant, as shown by the straight line

• Population death, like population growth, is generally
exponential or logarithmic

• The population will be reduced by the same fraction at
constant intervals

• When the population has been greatly reduced, the rate of
killing may slow due to the survival of a more resistant strain of the

Actions of
Microbial Control Agents

Alteration of
Membrane Permeability

• Damage to the lipids or proteins of the plasma membrane by
antimicrobial agents

• Causes cellular contents to leak into the surrounding
medium and interferes with the growth of the cell.

Damage to Proteins
and Nucleic Acids

• Damage to these nucleic acids by heat, radiation, or
chemicals is frequently lethal to the cell

• The cell can no longer replicate, nor can it carry out
normal metabolic function such as the synthesis of enzymes

of resistance


• Resistance of an organism to a sterilizing agent can be
described by means of the D-value

• Defined as ‘the time taken at a fixed temperature or the
radiation dose required to achieve a 90% reduction in viable cells’


• In order to assess the influence of temperature changes on
thermal resistance a relationship between temperature and log D-value can be
developed, leading to the expression of a z-value

• Represents the increase in temperature needed to reduce
the D-value of an organism by 90%

D-value and Z-value



• Physical methods

– Heat methods

Dry heat sterilization

Moist heat sterilization

– Radiation sterilization

• Chemical methods

• Mechanical methods

– Filtration sterilization 


• Sterilization is the removal or destruction of all forms
of microbial life

• Disinfection  
refers   to   the  
destruction   of  
vegetative   (non-
endospore-forming) pathogens

• Microbial death follows an exponential pattern

• Microbial control agents act by alteration of membrane permeability
or damage to proteins and nucleic Acids

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