Sterilization & Disinfection
23 Feb 23
By: Awoke D
Objectives
•After completion of this topic
students will be able to:
─Define and describe the
purpose and importance
sterilization and disinfection
─Discuss the different methods
of sterilization and disinfection
Contents
• Definition
• Purpose
• Methods of Sterilization
• Methods of Disinfection
• Summary
4
Terminologies
• Disinfection • Pasteurization
• Disinfectant • Tyndallization
• Antiseptic • Hot air oven
• Sterilization • Flaming
• Moist heat • Red eat
• Dry heat • Spore
• Incineration • Bactericidal
• Autoclaving • Bactriststatic
?
• What is sterilization and
disinfection?
• Purpose, methods…
• Discuss and share
Introduction
• Sterilization and disinfection are the basic components
of hospital infection control activities.
• Every day, a number of hospitals are performing various
surgical procedures.
• Even more number of invasive procedures are being
performed in different health care facilities.
• The medical device or the surgical instrument that comes
in contact with the sterile tissue or the mucus membrane
of the patient during the various processes is associated
with increased risk of introduction of pathogens
into the patient's body.
Intro…
• Moreover, there is chance of transmission of infection:
▫ From patient to patient;
▫ From patient or to health care personnel, and vice
versa; or
▫ From the environment to the patient through the
improper sterilized or disinfected devices.
• Hence, medical personnel, nurses, laboratory people and
the health care providers in general should have better
knowledge regarding these techniques to prevent the
spread of pathogens.
Definition
• Three different processes (cleaning, disinfection, and
sterilization) are commonly referred to as “disinfection”.
• There is no uniform definition or standard for sterilization,
disinfection, and cleaning.
▫ Cleaning reduces the number of
contaminants present and, in doing so,
removes a proportion of organisms
present .
▫ Removal of visible soil (e.g., organic and
inorganic materials) from the surfaces
and objects.
▫ Disinfection removes most pathogenic
organisms.
▫ Sterilization is the killing or removal of
all organisms.
Defn…
• Sterilization
• The process by which an article, surface or medium is
freed of all microorganisms either in the vegetative
or spore state.
Complete destruction of microorganism.
Defn…
• Sterilization is a term referring to any process that
eliminates or kills all forms of life, including fungi,
bacteria, viruses, spore forms present;
• On a surface,
• Contained in a fluid, in medication, or
• In a compound such as culture media.
• Sterilization can be achieved, for example, by
applying the proper combinations of heat,
chemicals, irradiation, high pressure, and
filtration.
Dfn…
• Disinfection: The process of destruction of pathogenic
microorganisms by direct exposure to chemical or
physical agents.
▫ The agents used to achieve these state is called
disinfectant.
Chemical disinfectants which can be safely applied to
living tissue (skin or mucous membrane) and are
used to prevent infection by inhibiting the growth of
bacteria are called antiseptics (eg. 70% ethanol).
• The choice between sterilization and disinfection must be
made according to the risk of spreading infection.
• Sterilization is required for all critical medical devices
–those intended to be used in contact with sterile tissues
– and recommended for semi-critical devices – Eg,
those intended to be in contact with mucous tissues or
non-intact skin.
• A high level of disinfection can still be acceptable for these.
Classification of devices into three categories depending on the
potential risk of transmission of infectious agents: critical, sem-
icritical, and noncritical
Increasing order of resistance of microorganisms to
sterilization and different levels of disinfectants
Applications
• Medicine/health service
• Food industry
Purpose
• Eliminate all microorganisms that will
come into contact with body tissues.
• Protect patients from possible
infection when natural defenses are
not normal.
• Commonly used in the operating
and delivery rooms.
▫ Sterilization for surgical procedures:
Gloves, aprons, surgical
instruments, syringes etc.
▫ Sterilization of culture media,
reagents & equipment to maintain a
sterile condition.
Methods of sterilization
• Physical (heat (dry, moist), light,
radiation)
• Mechanical (Filtration)
• Chemical
Germs
Physical method
1. Heat
• The use of heat is a very popular method of sterilization.
• The effect of heat depends on the time of exposure in
addition to form of heat that is supplied.
Example:
• The dry heat of an open flame incinerates
microorganisms (bacteria, fungi and yeast).
▫ Moist heat destroys microorganisms by the irreversible
denaturation of enzymes & structural proteins
(causing the microbial membranes to liquefy).
Heat
• Dry heat acts by;
• Protein
denaturation,
• Oxidative damage
• Toxic effects of
elevated
levels of electrolytes
• The moist heat acts by
coagulation and
denaturation of
proteins.
• Moist heat is superior
to dry heat in action.
Dry heat
• Red heat – inoculation loops, forceps edge, …
• Flaming – mouth of culture tubes, culture bottles with
medium, stoppers glass slides, cover slips, scalpel
needles.
• Hot Air Oven – Glasswares, metal & surgical instruments,
glass syringes, silicone rubber liners…@1600 C/1 hr.
The apparatus is heated by electricity or gas at the bottom
• Incineration – Wound swabs, dressings, clothing,
animal autopsies...
Incinerator
Moist heat
Sterilization by
Moist heat
Moist heat at Moist heat Moist heat
Below 100 0C At 100 0C above 100 0C
e.g.. Boiling
Pasteurization Tyndallization
Autoclave
63°-65°C for 30 min or to
73°-75°C for 15 seconds
Moist heat
1. At temperature <100°C
• Pasteurization of milk (63 0C 30’ (HM), 70 0C-
30’’(FM)), beverages, serum, body fluids (1hr at 56°C)
• Vaccine preparation -vaccine bath (1hr at 60°C)
2. At temperature 100°C
• Boiling - 100°C for 10’
• Single exposure at 100°C for
90 min kills thermophilic bacteria.
▫ Intermittent exposure at 100°C for
20-45 min on three successive days
kills spores, referred as -
‘TYNDALLISATION’.
3. At temperature >100°C
• Recommendations for sterilization in an autoclave are 15
minutes at 121⁰C @ 15 lbs pressure.
– 10 lbs pr. for 10 min (110°C)
– 30 lbs pr. for 3 min (134°C)
• All liquid culture media, cotton swabs,
inoculators, rubber corks….
Autoclave
Autoclave
2. Light : Direct sunlight for woolen, silk, cotton bed
spread, aprons, lab coats.
3. Radiation:
UV radiation – at 250nm wavelength or less,
biological safety cabinets, inoculation hood
or chambers, work – bench, room, operation
theaters, tissue culture glass wares.
Formation of thymine-thymine pairs on adjacent
DNA strands
γ rays – direct exposure
• Ionizing radiation
• Infrared radiation in ‘vacuo’ for surgical instruments
Radiation…
Exposure to electromagnetic radiation is a direct means of
killing bacteria.
• The energy of the radiation severs the strands of DNA in
many locations throughout the bacterial genome.
Mechanical Method: filtration
• Filtration is the physical removal of bacteria from a fluid by the
passage of the fluid through the filter.
• The filter contains holes of a certain diameter. If the diameter is
less than the smallest dimension of a bacterium, the bacterium
will be retained on the surface of the filter it contacts.
– HEPA (High Efficiency Particulate Air) filters for air
– Nitrocellulose or other known pore-size filters
– 0.45µm filters out most bacteria except
Mycoplasmas and other cell wall-less forms.
– 0.22µm will filter out all bacteria and spores.
Disinfection
• Disinfection refers to the reduction
in the number of living
microorganisms to a level that is
considered to be safe for the
particular environment.
• High-level disinfectants
• Kill most Mos except for spores.
• Glutaraldehyde (2%)
• H2O2 (3%-25%)
• Peracetic acid (0.2% to 8%)
• Hypochlorous acid
Carbolic
• Chlorine dioxide gas.
Steam Spray
Disinfection…
• Intermediary disinfectants
• Mainly used for noncritical items contaminated
with blood/body fluids
• Alcohols (70% to 90%)
• Iodophors (1% to 2% - 30ppm)
• Phenolic compounds (0.4% to 5%)
• Used in surface of instruments,
fibreoptic endoscopes, laryngoscopes,
vaginal specula, anesthesia circuits.
Disinfection…
• Low – Level disinfectants
• To remove the vegetative form of
bacteria, few fungi, and some
enveloped viruses from the noncritical
items like BP cuffs, ECG electrodes,
stethoscopes
• Quarternary NH4 compounds (0.4%
to 1.6%)
• Benzalkonium chlorine,
Cetylpyridinium chloride, denatures
cell membrane releases contents
out, bacteriocidal at high
concentration.
Detergents: (surface active
compounds) most notable the
quaternary ammonium compounds
like interact with membrane through
hydrophobic end disrupting
membrane.
Alcohols: disrupt membrane and
denature protein.
Phenols and derivatives: damage
membrane and denature proteins.
Agents modifying proteins
– Chlorine : oxidizing agent inactivating sulfhydryl-containing
enzymes .
– Iodine and iodophors (which have reduced toxicity): also
oxidation of sulfhydryl containing enzymes
– Hydrogen peroxide: oxidizing agent (sulfhydryl groups);
catalase inactivates
– Heavy metals: (silverand mercury) bind to sulfhydryl groups
inhibiting enzyme activity
– Ethylene oxide: alkylating agent (sterilizing agent)
– Formaldehyde and glutaraldehyde: denatures protein and
nucleic acids and alkylates amino and hydroxyl groups on both
Modification of nucleic adds
• Dyes: like crystal violet and malachite green whose positively
charged molecule binds to the negatively charged phosphate
groups on the nucleic acids.
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Summary
• Sterilization and disinfection are the basic components of
hospital infection control activities.
▫ Sterilization is the killing of all forms of microbial life.
▫ Disinfection is reducing the number of bacteria to a
level low enough that disease is unlikely to occur.
• Methods
▫ Physical agents kill (or remove) organisms by one of the
three methods: Heat, radiation, or filtration.
▫ Chemical agents kill bacteria by one of three actions:
Disruption of lipid in cell membranes, modification of proteins,
or modification of DNA.
Thank you!
