Disinfection and Sterilisation

Disinfection &
Sterilization
( Dafae Ta’affun & Amale Tatheer )
Dr Md Tanwir Alam, MD
Assistant Professor, Dept. of PCM,
Govt. Tibbi College & Hospital, Patna
05/19/2020 tanveernium@gmail.com 1

Contents
• Objectives
• Historical background
• Introduction
• Types of disinfection
• Factors Affecting Disinfection
• Methods Of Disinfection & Sterilization
✓ Natural Methods
✓ Physical Methods
✓ Chemical Methods

Objectives
Define [bactericidal, bacteriostatic, sterilization,disinfection]Define
Classify and enumerate different methods of sterilizationClassify
Explain the principle and applications of each typeExplain
Enumerate categories of disinfectantsEnumerate

Historical background
• The scientific use of disinfection and sterilization methods
originated more than 100 years ago.
• Ignatz Semmelweis (1816-1865) and Joseph Lister (1827-
1912) - important pioneers for the promotion of infection
control.

• More than 100 years ago, Semmelweis demonstrated that routine hand
washing can prevent the spread of disease.
• He worked in a hospital in Vienna where maternity patients were dying at
an alarming rate.
• He recognized that medical students worked on cadavers during an
anatomy class and afterwards they went to the maternity ward.
• Students did not wash their hands between touching the dead and the
living!!!
• After administrating the hand washing before examining the maternity
patients the mortality rate decreased.

• Lister, for the first time, used carbolic acid in operating theatres that
significantly reduced mortality rates.
• In 1867, Lister introduced the use of phenol as antimicrobial agent for
surgical wound dressings.
• His principles were gradually adopted in Britain and later in US.
• This was the beginning of infection control.

◼ Denature bacterial proteins and dissolves lipids

Definitions
Bactericidal kills bacteria
Bacteriostatic inhibits growth of bacteria

Definitions
Sterilization removal or killing of all living microorganisms
including bacteria and their spores
Disinfection removal or killing of disease-causing
microorganisms
(not necessarily all microorganisms)
or
Thermal or chemical destruction of pathogens &
other types of microorganisms.

Definitions
Disinfectants Usually a chemical agent (but physical) that
destroys all diseases causing pathogens or
other harmful microorganisms except bacterial
spores ; (applied to inanimate objects)
Antiseptic Substance that prevents or arrest the growth or
action of micro organisms by inhibiting their
activity or by destroying them.
The term is used especially for preparation
applied topically by living tissues

▪ The process of freeing an article or a surface from all or some
of the living microorganisms but not necessarily bacterial
spores
▪ Strong disinfectants: for inanimate object
▪ Mild disinfectant (antiseptic): superficial application on living
tissue
Disinfection

Definitions
Asepsis Prevention of contact with micro organisms
Sanitizer Agent that reduce the number of bacterial
contaminants to safe level as judge by public
health requirements.
Commonly used with substances applied to
inanimate objects

Definitions
Sterile State of being free from all living microorganism
Germicide Agent that destroys micro organisms, especially
pathogenic organism

DefinitionsDetergent Surface cleaning agent that makes no antimicrobial
claims on the level.
They comprise a hydrophilic component and a lipophilic
component
It acts by lowering surface tension e.g., soap – removes
bacteria along with dirt
Cleaning Removal, usually with detergent and water or enzyme
cleaner and water, of adherent visible soil, blood, protein
substances, micro organisms and other debris from the
surfaces by a manual or mechanical process that prepares
the items for safe handling and/or further
decontamination

Definitions
Deodorant Substance which suppresses or neutralize bad
odours eg.- lime, Ble. powder
Hospital
Disinfectant
Those registered to use in hospital/clinics/dental
and other medical facility efficacy to demonstrate
against salmonella, Choleraesuis, Staphylococcus,
and Pseudomonas aeruginosa

SHOULD
BE
Broadly
active
Killing pathogens
Not
Harmful
Good
Penetration
No damage to
non-living
material
Easily to work
with
Stable &
Resistant to
inactivation

Ideal disinfectant
• Highly efficacious
• Fast
• Good penetration
• Compatible with most materials
• Non-toxic
• Effective despite presence of organic material.
• Residual effect
• Economical
• Odourless

Microbe type
(e.g., Mycobacteria, spores,
and certain viruses) very
resistant
Nature and Number of
Cells
Vegetative cells in log
phase, Easy to kill
Substrate effects
(high organic content
interferes with disinfection)Density
It’s easier (and faster) to kill
fewer microbes than many
microbes
Dependents on: Conc., length (time), temperature Chemical
reaction 2x increase in rate with each 10°C

Types of disinfection
• Concurrent disinfection:
✓ Application of disinfective measures as soon as possible after the
discharge of infectious material from the body of an infectious
person.
✓ Consists of disinfection of urine, faeces, vomit, clothes, hands,
dressings, apron, gloves.
• Terminal disinfection:
✓ Application of disinfective measures after the patient has died or has
ceased to be a source of infection.
• Percurrent (prophylactic) disinfection:
✓ Disinfection of water by chlorine, pasteurization of milk, hand
washing.

Types of disinfectants
• High-level disinfectants
✓ aactivity against bacterial spores
• Intermediate-level disinfectants
✓ tuberculocidal activity but not sporocidal
• Low-level disinfectants
✓ a wide range of activity against microorganisms but no
sporocidal or tuberculocidal activity

Types of materials in healthcare
Critical materials
✓ invade sterile tissues or enter the vascular system.
✓ most likely to produce infection if contaminated and
therefore require sterilization.
➢ E.g. Surgical instruments, cardiac catheters

Types of materials in healthcare
Semicriticial materials
✓ have contact with mucous membranes
✓ require high-level disinfection agents
➢ E.g. cystoscope, laryngoscope blade.
Noncriticial materials
✓ have contact with intact skin
✓ require intermediate-level to low-level disinfection
➢ E.g. bedpans , BPCuffs

Methods of disinfection
• Natural methods
• Physical methods
• Chemical methods

Natural agents
• Sunlight
✓ UV rays of sunlight lethal to bacteria and some viruses.
✓ Articles such as linen, bedding and furniture may be disinfected.
• Air
✓ Acts by drying or evaporation of moisture which is lethal to most bacteria.
• Burning
✓ Inexpensive articles such as contaminated dressings , rags and swabs –
disposed off by burning.
✓ Best done in an incinerator.
✓ Addition of sawdust, paper, kerosene or other combustible material aid in
burning.

Physical agents
• Hot air
✓ Articles such as glassware, syringes,
swabs, dressings and sharp instruments.
✓ Drawback – no penetrating power: not
suitable for bulky materials.
✓ Hot air oven – temp 160-180 deg C for
at least 1hour to kill spores.
Hot air oven

Physical agents
• Thermal Death Point (TDP):
✓ Lowest temperature at which all of the microbes in a liquid suspension
will be killed in ten minutes.
• Thermal Death Time (TDT)
✓ Minimal length of time in which all bacteria will be killed at a given
temperature.
• Decimal Reduction Time (DRT)
✓ Time in minutes at which 90% of bacteria at a given temperature will
be killed. Used in canning industry.

Physical agents
• Moist Heat
✓ Kills by denaturing proteins and destroying cytoplasmic membranes.
✓ More effective than dry heat; water better conductor of heat than air.
✓ Methods of microbial control using moist heat
➢ Boiling
➢ Autoclaving
➢ Pasteurization

Physical agents
• Boiling
✓ for 5-10 minutes :kill bacteria but not spores or viruses.
✓ Temp. above 100 deg C required for destruction of spores.
✓ Disinfection of small instruments, tools not used for subcutaneous
insertion, linen and rubber goods such as gloves.
✓ Slow process, unsuitable for thick beddings and it fixes albuminous
stains.

Physical agents
• Autoclaving
✓ Operate at high temperature and pressure.
✓ Destroys all forms of life, including spores.
✓ Sterilization of linen, dressings, gloves, syringes, instruments and
culture media.
✓ Not suitable for plastics and sharp instruments.

Autoclave

Physical agents
• Pasteurization
✓ A process in which fluids are heated at temperatures below boiling point to
kill pathogenic microorganisms in the vegetative state without altering the
fluid’s palatability.
✓ Conditions: 62℃, 30min or 71.7℃, 15sec
✓ Significance: kills vegetative pathogens.

Pasteurisation

Physical agents
• Radiation
✓ Sterilization of bandages , dressings , catgut and surgical
instruments.
✓ Great penetrating power with little or no heating effect.
✓ Most effective ,but very costly.
✓ Normally carried out by gamma radiation.

Physical agents
• Filtration
✓ Removal of microbes by passage of a liquid or gas through a screen like
material with small pores. Used to sterilize heat sensitive materials like
vaccines, enzymes, antibiotics, and some culture media.
✓ 0.22 and 0.45um Pores: Used to filter most bacteria. Don’t retain
spirochetes, mycoplasma and viruses.
✓ 0.01 um Pores: Retain all viruses and some large proteins

Examples of disinfectant and antiseptics
There are a number of chemicals that can act as disinfectants or
antiseptics. These include:
✓ Phenol and its derivatives e.g. Dettol.
✓ Halogens e.g. Chlorine, Tincture iodine.
✓ Alcohols e.g. ethyl alcohol.
✓ Aldehydes e.g. glutaraldehyde (Cidex), Formalin.
✓ Quaternary Ammonium Compounds (Cationic detergents).

Halogen
Halogen Phenol
derivative

Chemical agents
• Phenol and related compounds
✓ Intermediate- to low-level disinfectants
✓ Denature proteins and disrupt cell membranes
✓ Effective in presence of organic matter and remain active for
prolonged time.
✓ Commonly used in health care settings, labs, and homes (Lysol, triclosan)
✓ Have disagreeable odor and possible side effects.

Chemical agents
• Phenol (carbolic acid)
✓ not an effective disinfectant
• Crude phenol
✓ phenol and cresol. effective against gram +ve and –ve organisms.
• Cresol
✓ used in 5 to10 % for disinfection of urine and faeces.
• Cresol emulsions
✓ very powerful disinfectants

Chemical agents
• Chlorhexidine (hibitane)
✓ most useful skin antiseptic. 0.5% solution used as handlotion.1% creams
used for burns
• Hexachlorphane
✓ slow in action , but shows cumulative effect on skin and is compatible
with soaps.
• Dettol (chloroxylenol)
✓ relatively non toxic antiseptic. 5% Dettol for disinfection of instruments
and plastic equipments.

Chemical agents
Quaternary ammonium compounds
• Cetrimide(cetavlon)
✓bactericidal against vegetative gram +ve organisms, much less
against gram -ve
✓ Used in 1-2 % strength
• Savlon
✓ Combination of cetavlon and hibitane .
✓ Plastic appliances may be disinfected in 20 min.
✓ Disinfection of clinical thermometers in 3 minutes.

PHENOLICS
Carbolic acid: 2 - 5%
Powerful microbicidal, very corrosive
General purpose disinfectant in hospital
Stable, persistant, and especially effective when dealing
with disinfecting materials contaminated with little
organics
Cresol, lysol
➢Chloroxylenol, chlorophenol, hexachlorophane less
toxic, less irritant, less active, more readily inactivated by
organic matter

➢ Affect plasma membrane,
inactivates enzymes, and denature
proteins
➢ Leave residual films, can irritate
skin, don’t kill endospores, and
are corrosive to rubber and
plastics
➢ Some phenolics are mild enough
for use as antiseptics while others
are too harsh or otherwise
dangerous to be employed on
living tissue
PHENOLICS
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05/19/2020 47

Chemical agents
• Halogens and their compounds
✓ Intermediate-level antimicrobial chemicals
✓ Believed that they damage enzymes via oxidation or by denaturing them.
✓ Iodine tablets, iodophores (Betadine®), chlorine treatment of drinking water,
bleach, chloramines in wound dressings, and bromine disinfection of hot
tubs.

HALOGENS
Kills by oxidation
✓ Iodine: 2.5% in 70% alcohol, Skin antiseptic
✓ Iodophores: (iodine + non-ionic surface active agent) –
betadine – non staining, less irritant, less toxic
✓ Chlorine: disinfect water supplies, swimming pools
✓ Sodium hypochlorite: 1% for HIV
✓ Organic chloramines: antiseptic for wound dressings
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Halogens
➢ Iodine: commonly used as an antiseptic against
all microbes, fungi, and viruses
➢ Iodine: It inhibits protein synthesis and oxidizes
–SH groups of amino acids
➢ Chlorine: Used as a disinfectant (10% bleach)
➢ Chlorine: Hypochlorous acid (HOCl) is a product,
formed in water, that is the active form of the
disinfectant
Cl2 + H2O ------> H+ + Cl- + HOCl
Hypochlorous acid

Chemical agents
• Alcohols
✓ Intermediate-level disinfectants.
✓ Denature proteins and disrupt cytoplasmic membranes.
✓ Evaporate rapidly.
✓ Swabbing of skin with 70% ethanol prior to injection.

Chemical agents
• Isopropyl Alcohol (70%)
✓ Powerful disinfectant and antiseptic
✓ Mode of action: denatures proteins, dissolves lipids and can lead to cell
membrane disintegration
✓ Effectively kills bacteria and fungi
✓ But does not inactivate spores!

Chemical agents
• Aldehydes
✓ Denature proteins and inactivate nucleic acids.
✓ Glutaraldehyde both disinfects (short exposure) and sterilizes (long
exposure)
✓ Formalin used in embalming and disinfection of rooms and instruments.

Chemical agents
• Formaldehyde
✓ Highly toxic and irritant gas
✓ Effective against vegetative bacteria ,fungi and many viruses.
✓ Used as a 2-3 % solution for spraying rooms, walls and furniture
✓ Most effective at a high temperature and relative humidity of 80-90%

Chemical agents
• Oxidizing agents
✓ Peroxides, ozone, and per acetic acid kill by oxidation of microbial
enzymes
✓ High-level disinfectants and antiseptics
✓ Hydrogen peroxide can disinfect and sterilize surfaces of objects.
✓ Ozone -treatment of drinking water.
✓ Per acetic acid – effective sporocide used to sterilize equipment.

Chemical agents
• Surfactants
✓ Surface active chemicals that reduce surface tension of solvents to make
them more effective at dissolving solutes
✓ Soaps and detergents
✓ Colorless, tasteless, harmless to humans, and antimicrobial; ideal for
many medical and industrial uses.
✓ Low-level disinfectants.

Chemical agents
• Metals
✓ Ions are antimicrobial because they alter the 3-D shape of proteins,
inhibiting or eliminating their function.
✓ Low-level bacteriostatic and fungistatic agents.
✓ 1% silver nitrate to prevent blindness caused by
➢ N. gonorrhoeae .
✓ Thiomersal (mercury-containing compound) used to preserve vaccines.

Oligodynamic action of Heavy Metals
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Heavy Metals or Metallic Salts
Most common: Ag, Cu, Hg (ointment), Ni, Zn,
Ag(NO3)2, CuSO4 , ZnCl2, HgCl2
➢ Oligodynamic action: exert antimicrobial activity
➢ React with sulfhydral (–SH) groups of proteins,
denaturing proteins
➢ Silver nitrate is used to treat Ophthalmia
neonatorum in newborns as caused by Neisseria
gonorrhoeae (gonorrheal eye infections)
➢ Copper salts: antifungal, antialgae – water
reservoirs, swimming pools

Heavy Metals or Metallic Salts
❑ Mercury: Organic mercury compounds like merthiolate
and mercurochrome are used to disinfect skin wounds.
❑ Selenium
➢ Kills fungi and their spores. Used for fungal infections.
➢ Also used in dandruff shampoos.
❑ Zinc
➢ Zinc chloride is used in mouthwashes.
➢ Zinc oxide is used as antifungal agent in paints.
05/19/2020 61

Chemical agents
Lime
✓ Cheapest disinfectant
✓ Used as fresh quick lime or 10-20 % aqueous suspension known as
milk of lime.
✓ Faeces and urine disinfected by 10-20% aqueous solution (in 2 hrs).
✓ Used as a deodorant in public places where toilets are located.

Chemical agents
Ethylene oxide
✓ for heat sensitive articles
✓ At 55- 60 deg C : kills bacteria, spores and viruses.
✓ Mixed with 12 % carbon dioxide (as it is explosive)
✓ Water vapor added to the mixture to increase efficacy.
✓ To sterilize fabrics, plastic equipment, cardiac catheters etc.

Some Newer agents
• Bacillocid® rasant
✓ Formaldehyde-free disinfectant cleaner with low use concentration
• Virkon
✓ gaining importance as non Aldehyde compound
✓ Disinfects medical devices and lab equipments.
✓ Decontaminate spillages with Blood and body fluids.

Gas plasma sterilization
• Gas plasma generated in an enclosed chamber under deep
vacuum using Radio frequency or Microwave.
• Can be used for hand sterilization.
• The mechanism of action of this device is the production of
free radicals within a plasma field that are capable of
interacting with essential cell components

Sterilization Control
• To ensure that potentially infectious agents are destroyed by adequate
sterilization regimes
• Three levels:
• Physical: measuring device control (temp., time, pressure)
• Biological
• Chemical

Introduction
• Sterilization
✓ Destruction of all forms of life, including the bacterial spores,
viruses, prions
✓ No degrees of sterilization: an all-or-nothing process.
✓ Physical or chemical methods.

Methods of Sterilization
Heat
Sterlization
Dry Heat
Red Heat
Flaming
Incineration
Hot Air Oven
Moist Heat
Below 100 °C  Pasteurization
At 100 °C  Boiling
Above 100 °C  Autoclaving

Sterilization by heat
• Heat is the most practical, reliable, and inexpensive method of
sterilization.
• It is used for sterilization of objects and materials that can withstand
high temperatures.
• It can be either:
✓ Dry heat
✓ Moist Heat

1. Red Heat
Principal:
Holding object in
Bunsen flame till they
become red hot.
Used for:
Sterilization of:
• Bacteriological
loops
• Tips of forceps

2. Flaming
Principal:
Passing the object
through the flame of
Bunsen burner without
heating to redness.
Used for:
Sterilization of:
✓ glass slides
✓ mouth of culture
tubes.

3. Incineration
Principal:
Infective materials is
converted to sterile ash
by burning in
incinerator
Used for:
Destruction of
contaminated
disposable materials
(waste)

Hot air oven05/19/2020 tanveernium@gmail.com 73

4. Hot air oven
Principal
✓ Articles to be sterilized are
exposed to high temperature in
an electrically heated oven.
✓ Even distribution of heat
throughout the chamber is
achieved by a fan.
Holding time:
✓ 160°C for two hour
✓ 180°C for one hour

Hot air oven
Used for Sterilization of:
✓ All glasses: test tubes, Petri dishes,
flasks, pipettes.
✓ Instruments: as forceps, scalpels, scissors
✓ Dry material in sealed containers as fat,
oils, powder.

Moist Heat
Can be used at different temperatures:
✓ Below 100 °C
✓ At 100 °C
✓ Above 100 °C
✓ Pasteurization
✓ Boiling
✓ Autoclave

1. Pasteurization (Below 100)
Principal:
Pasteurization is a
process of heating a
liquid to a specific
temperature for a
definite length of time
and then cooling it
immediately.
Used for:
Pasteurization is
commonly used in milk
processing.

2. Boiling (At 100 °C)
Principal:
Boiling in water for fifteen minutes will
kill most vegetative bacteria and
inactivate viruses.
However boiling is ineffective against
many bacterial and fungal spores.
Used for:

3. Autoclaving
Principal:
• When the pressure is increased inside a closed
container, the temperature at which water boils exceeds
100°C.
• At double atmospheric pressure the temperature of the
steam reaches 121°C.
• Autoclaving is the most reliable method of sterilization
that kills all kinds of bacteria and spores.

3. Autoclaving
Temperature of sterilization:
- 121C for 20 – 30 minutes.
Used for sterilization of:
• Culture media.
• Surgical supply e.g. dressing, and surgical
instruments.

Filtration
It is possible to remove bacteria
from fluids by passing them
through filters with pores so
small that bacteria are arrested.

Filtration
✓ Filtrations is used to sterilize
liquids that would be damaged
by heat as sera, antibiotic
solutions and vaccines.

Ionizing irradiation (gamma rays)
• Used for sterilization of an
article not stand heat as
rubber catheters, gloves,
plastic syringes.

Factors that influence the degree of killing
✓ Types of organisms
✓ Number of organisms
✓ Concentration of disinfecting agent
✓ Presence of organic material (e.g., serum, blood)
✓ Nature (composition) of surface to be disinfected
✓ Contact time
✓ Temperature
✓ pH
✓ Biofilms
✓ Compatibility of disinfectants and sterilants

• Type of organisms
✓ Organisms vary in their ability to withstand chemical and physical
treatment, e.g.,
➢ Spores–have coats rich in proteins, lipids and carbohydrates
➢ Mycobacteria–cell walls are rich in lipids
➢ Prions–the most resistant known organisms to the action of heat,
chemicals, and radiation.

• Number of organisms
✓ Microbial load-the total number of organisms which determine the
exposure time of killing agent
✓ organisms have varying degrees of susceptibility to killing agents
✓ not all organisms die at the same time
✓ the death curve is logarithmic!!!
✓ higher numbers of organisms require longer exposure.

• Concentration of disinfecting agent
✓ a proper concentration of disinfecting agents ensure the killing of target
organisms, e.g.,
✓ povidone-iodine should be diluted with water before use because there is not
enough free iodine to kill microorganisms in concentrated solution.

• Presence of organic material
✓ such as blood, mucus, pus affects killing activity by inactivating the
disinfecting agent, e.g,
✓ by coating the surface to be treated, prevents full contact between object
and agent (Glutaraldehyde)
✓ For optimal killing activity, instruments and surfaces should be cleansed
of excess organic material before disinfection !!!

• Nature (composition) of surface to be disinfected
✓ some medical instruments are manufactured of biomaterials that exclude
the use of certain disinfection and sterilization methods because of
possible damage, e.g.,
✓ endoscopic instruments cannot be sterilized by the heat in an autoclave.

• Contact time
✓ the amount of time a disinfectant or sterilant is in contact with the object
is critical e.g.,
✓ Betadine must be in contact with object for at least 1 to 2 min
to kill microbes.
✓ the spores of bacteria and fungi need a much longer time
✓ determine whether it is disinfecting or sterilizing the object.

• Biofilms
✓ communities of microorganisms.
✓ can be on a surface of either inanimate or animate objects, e.g,
catheters , pipes that carry water.
✓ make disinfection more difficult.
✓ the concentration of the disinfectant and the contact time need to
be increased.

• Compatibility of disinfectants
✓ a common mistake is to believe that two disinfectants are
better than one !
✓ some of them may inactivate other, e.g.,
✓ the bleach and quaternary ammonium compound together negate the
activity of both.

Sterilization Control
• Biological:
✓ Bacillus stearothermophilus spores(104-106 organisms)
✓ survives steam heat at 121ºC for 5 min. and is killed at 121ºC in 13
min.
✓ validate and determine the adequacy of steam or chemical sterilization.
✓ Bacillus subtilis/B.atrophaeus spores
✓ validate and determine the adequacy of ethylene oxide or dry heat
sterilization.

Chemical Indicators
• Browne's tubes are glass tubes that contain heat sensitive
dyes. These change color after sufficient time at the desired
temperature.
• Before heat exposure, the contents of the tube appear red.
• As heating progresses, the color changes to green.

Chemical Indicators
✓ Bowie Dick tape is
applied to articles
being autoclaved.
Before heat exposure,
the tape is uniformly
buff in color.
✓ After adequate heating,
the tape develops dark
brown stripes.
The pack on the left has been properly
sterilized; that on the right has not.

Some PracticalAspects
• Disinfection of faeces & urine-
✓ Collected in impervious container.
✓ Add equal volume of disinfectant for 1-2 hrs.
Disinfectant Amount per litre Percent
Bleaching
powder
50 gms 5
Crude phenol 100ml 10
Cresol 50 ml 5
Formalin 100 ml 10

Disinfection of faeces & urine
✓ Quick lime or milk of lime can be used if above disinfectants
not available.
✓ Bedpans and urinals – steam disinfected.

Disinfection of sputum
✓ Received in gauze or paper handkerchief.
✓ Destroyed by burning.
✓ Disinfected by boiling or autoclaving for 20 min at 20 lbs
pressure.
✓ Or 5 % cresol can be used.

• Disinfection of blood/body fluids spills
✓ Clean the affected area with soap and water then disinfect with a 1%Na
hypochlorite solution for 15 minutes.
• HIV infected articles
✓ Cleaning and 2% glutaraldehyde for 30 minutes.
✓ 6% Hydrogen peroxide for 30 minutes.
✓ 1% hypochlorite solution for 30 minutes.

Fumigation
✓ To sterilize the operation theatre formaldehyde gas (bactericidal
& sporicidal, viricidal) is widely employed as it is cheaper for
sterilization of huge areas like operation theatres.
✓ Formaldehyde is irritant to eye & nose; and it has been
recognized as a potential carcinogen.

Quick Revision

MCQs

1. Sterilization in autoclave is considered
Sterilization by:
A. Dry heat
B. Moist heat
C. Irradiation
D. Filtration

2. Sterilization in autoclave is doneat
temperature of:
A. 121C for 20 minutes
B. 180C for 2 hours
C. 180C for 20 minute
D. 121C for 2 hours

3. Dry heat sterilization can beachieved
by:
A. Autoclave
B. Hot air oven
C. Boiling
D. Incubator

4. Moist Heat sterilization can beachieved
by:
A. Autoclave
B. Incineration
C. Flaming
D. Hot air oven

5. An agent that inhibit the growthof
bacteria is:
A. Bactericidal
B. Bacteriostatic.

6. Bacteriostatic agent means:
A. Which inhibit growth of bacteria.
B. Which stimulate growth of bacteria.
C. Which kills the bacteria.

7. Sterilization in Hot air oven is doneat:
A. at 121C for 20 minutes
B. at 180C for 2 hours
C. at 180C for 20 minute
D. at 160C for 2 hours.

8. How can you sterilize culturemedia
A. Boiling
B. Incineration
C. Autoclaving
D. Hot air oven
E. Filtration
F. UV radiation.

9. How can you sterilizesera
A. Boiling
B. Incineration
C. Autoclaving
D. Hot air oven
E. Filtration
F. UV radiation

10. How can you sterilizeOil/powders
A. Boiling
B. Incineration
C. Autoclaving
D. Hot air oven
E. Filtration
F. UV radiation

11. How can you sterilizeBacteriological loops
A. Boiling
B. Red Heat
C. Autoclaving
D. Hot air oven
E. Filtration
F. UV radiation
G. Gamma rays

12. How can you sterilize interiorsof
biological safety cabinets:
A. Boiling
B. Incineration
C. Autoclaving
D. Hot air oven
E. Filtration
F. UV radiation
G. Gamma rays

13. How can you sterilize glassware e.g.test
tubes:
A. Boiling
B. Incineration
C. Hot air oven
D. Filtration
E. UV radiation
F. Gamma rays

14. How can you sterilize plasticsyringes:
A. Boiling
B. Incineration
C. Hot air oven
D. Filtration
E. UV radiation
F. Gamma rays

15. True or False
A. Bactericidal inhibits growth of bacteria
B. Bacteriostatic inhibits growth of bacteria
C. Sterilization is the removal or killing of
disease-causing microorganisms
D. Disinfection is the removal or killing of
disease-causing microorganisms
E. Objects can be sterilized in hot air oven
at 160°C for 20 minutes

16. Skin can be sterilized byusing:
A. Antibiotics
B. Disinfectant
C. Irradiation
D. Antiseptic

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Disinfection and Sterilisation

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