Sterilisation Physical agent Flashcards
(33 cards)
Define Sterilization and Disinfection
Sterilization is defined as the process by which an article, surface or medium is freed of all living microorganisms (Sporing and non sporing bacteria, viruses, fungi and protozoa) either in the vegetative or spore state.
Disinfection means the destruction or removal of all pathogenic organisms, or organisms capable of giving rise to infection
What are the uses of sterilization and Disinfection?
in microbiology for preventing contamination by extraneous organisms,
in surgery for maintaining asepsis,
in food and drug manufacture for ensuring safety from contaminating organisms.
Explain the terms a. Antisepsis b. Antiseptics c. Bacteriostatic agents d. Decontamination
antisepsis is used to indicate the prevention of infection, usually by inhibiting the growth of bacteria in wounds or tissues.
Antiseptics are chemical disinfectants, which can be safely applied to skin or mucous membrane and are used to prevent infection by inhibiting the growth of bacteria.
Bacteriostatic agents only prevent the multiplication of bacteria, which may however remain alive.
Decontamination refers to the process of rendering an article or area free of danger from contaminants, including microbial, chemical, radioactive and other hazards.
What are the Physical agents of sterilisation and disinfection?
1.Sunlight
2. Drying
3. Dry heat: flaming, incineration, and hot air.
4. Moist heat: pasteurization, boiling, steam under normal pressure, and steam under pressure.
5. Filtration: candles, asbestos pads, membranes.
6. Radiation.
7. Ultrasonic and sonic vibrations.
Name the Chemicals agents used in sterilisation and disinfection
Ethylene oxide, Formaldehyde, Betapropiolactone , Alcohols, Aldehydes, Dyes, Halogens, Phenols, Surfaceactive agents, Metallic salts etc.
What is Wet sterilization?
Sterilisation using steam or water at high temperature
What is Dry sterilisation?
sterilisation using hot air
Define thermal death time
minimum time required to kill a suspension of organisms at a predetermined temperature in a specified environment.
Explain various dry heat sterilisation methods
Flaming:
Inoculating loop or wire, the tip of forceps and searing spatulas are held in a Bunsen flame till they become red hot.Inoculation loops carrying infective material may be dipped in a disinfectant before flaming to prevent spattering.
Incineration
excellent method for safely destroying materials such as contaminated cloth, animal carcasses, and pathological materials that can be burnt.
Hot air oven
electrical devices
developed by Louis Pasteur.
uses dry heat to sterilize articles
most widely used method
is fitted with a fan to ensure even distribution of air and elimination of air pockets.
heated by electricity, with heating elements in the wall of the chamber.
The material to be sterilised :glass wares, forceps, scissors, scalpels, all-glass syringes, swabs , pharmaceutical products such as liquid paraffin, dusting powder, fats and grease in small containers.
- Explain various moist heat sterilisation methods
Temperatures below 1000
C:
Pasteurization of milk: originally employed by Louis Pasteur.employed in food and dairy (milk and milk products) industry.There are two methods:
Holder method: The temperature employed is 630
C for 30 minutes
❖ Flash process: The temperature
employed is 720
C for 15-20 seconds
❖ Both methods are followed by cooling
quickly to 100
C or lower
❖ Destroy all nonsporing pathogens
❖ Coxiella burnetti may survive the holder method
Vaccine bath: Vaccines of nonsporing
bacteria are heat inactivated in special
vaccine bath at 60 o C for 1 hour
Serum bath: Serum or body fluids can be
sterilized by heating for one hour at 560
C
in a water bath for several days
Inspissation: Media such as LJ are
sterilized at 80-85 0
C for half an hour on
three successive days in an inspissator
• On the first day, the vegetative bacteria
would die and those spores that
germinate by next day are then killed the following day.
Temperature at 100 0
C:
Boiling:
▪ Vegetative bacteria are killed immediately
at 90-1000
C
▪ Material should be immersed in the water
and boiled for 10-30 minutes
Boiling is not recommended for the
sterilization of instruments used for
surgical procedures
▪ Autoclaving at high pressure can destroy
spores and ensure sterilization
Steam at atmospheric pressure (1000
C):
Free steam:
❖ Used to sterilize culture media, which
may decompose if subjected to higher
temperatures
❖ A single exposure of ninety minutes
usually ensures sterilization
❖ Ex: Koch or Arnold steamer
Tyndallization: (Intermittent heating)
• For media containing sugars or gelatin an
exposure of 1000
C for 20 minutes on three
successive days is used
• Principle is that the first exposure kills all
vegetative bacteria
• Spores, since they are in a favorable
medium, will germinate
• Will be killed on the subsequent occasions
• May fail with spores of certain anaerobes
and the thermophiles
Moist heat above 100 0 C (Steam under
pressure):
Autoclave:
A strong, pressurized,Steam heated vessel
for Sterilization or cooking
Principle:
• Water boils when its vapour pressure
(pressure exerted by a vapour on the
surface of the liquid) equals that of
surrounding atmosphere
• Hence when pressure inside a closed
vessel increases, the temperature at
which water boils also increases
• Saturated steam thus produced has
penetrative power
• When steam comes into contact with a
cooler surface it condenses to water
Gives up its latent heat (The quantity of
heat absorbed or released by a substance
undergoing a change of state) to that
surface
• Process continues till the temperature of
that surface is raised to that of steam
• This result in the denaturation and
coagulation of protein inside the
microorganism
• Usual holding time is 121 0C for 15
minutes at 15 PSI
Simple laboratory Autoclave:
• Consists of a vertical or horizontal
cylinder of gunmetal or stainless steel, in
a supporting sheet iron case
• Lid or door is fastened by crew clamps
• Made airtight by an asbestos washer
Autoclave has on its lid or upper side:
• A discharge tap for air and steam
• A pressure gauge
• A safety valve
• Heating is by
gas or electricity
What are the factors which affect the sterilisation? How it affect sterilisation?
Nature of heat: Moist heat is more
effective than dry heat.
• Temperature and time: temperature and
time are inversely proportional
• Number of microorganisms: More the
number of microorganisms, higher the
temperature or longer the duration
required
Nature of microorganism: Depends on
species and strain of microorganism,
sensitivity to heat may vary
• Spores are highly resistant to heat
• Type of material: Articles that are heavily
contaminated require higher temperature
or prolonged exposure
• Certain heat sensitive articles must be
sterilized at lower temperature
• Presence of organic material: Protein,
sugars, oils and fats increase the time
required for sterilisation
• The presence of disinfectants and high
acid or alkaline pH speed up the bacterial
killing
What is Pasteurization?
This process was originally employed by Louis Pasteur. Currently this procedure is employed in food and dairy (milk and milk products) industry. There are two methods.
Holder method: The temperature
employed is 630
C for 30 minutes
❖ Flash process: The temperature
employed is 720
C for 15-20 seconds
❖ Both methods are followed by cooling
quickly to 100
C or lower
❖ Destroy all nonsporing pathogens
❖ Coxiella burnetti may survive the holder
method
What is Vaccine bath?
Vaccines of nonsporing
bacteria are heat inactivated in special
vaccine bath at 60 o C for 1 hour
What is Serum bath?
Serum bath: Serum or body fluids can be
sterilized by heating for one hour at 560
C
in a water bath for several days
What is Inspissation?
Media such as LJ are
sterilized at 80-85 0
C for half an hour on
three successive days in an inspissator
• On the first day, the vegetative bacteria
would die and those spores that
germinate by next day are then killed the
following day.
What is Tyndallization?
For media containing sugars or gelatin an
exposure of 1000
C for 20 minutes on three
successive days is used
• Principle is that the first exposure kills all
vegetative bacteria
• Spores, since they are in a favorable
medium, will germinate
• Will be killed on the subsequent occasions
• May fail with spores of certain anaerobes
and the thermophiles
What is Flaming and its uses?
Inoculating loop or wire
✔ Tip of forceps
✔ Searing spatulas are held in a Bunsen
flame till they become red hot
✔ Inoculation loops carrying infective
material may be dipped in a disinfectant
before flaming
What is Incineration ?
Excellent method for safely destroying
materials such as:
ø Contaminated cloth
ø Animal carcasses
ø Pathological materials
ø Polystyrene materials emit clouds of
dense black smoke
ø Hence should be autoclaved in
appropriate containers
What is boiling? What is its disadvantage?
Vegetative bacteria are killed immediately
at 90-1000
C
▪ Material should be immersed in the water
and boiled for 10-30 minutesBoiling is not recommended for the
sterilization of instruments used for
surgical procedures
▪ Autoclaving at high pressure can destroy
spores and ensure sterilization
What is free steam sterilisation? Give one example
Used to sterilize culture media, which
may decompose if subjected to higher
temperatures
❖ A single exposure of ninety minutes
usually ensures sterilization
❖ Ex: Koch or Arnold steamer
Write a note on hot air oven
It is an electrical devices used in
sterilization
• Developed by Louis Pasteur
• The oven uses dry heat to sterilize articles
• Most widely used method of sterilization
by dry heat
• Oven is fitted with a fan to ensure even
distribution of air and elimination of air
pockets
• The oven is usually heated by electricity,
with heating elements in the wall of the
chamberThe material to be sterilised under this
method include
• Glass wares
• Forceps
• Scissors
• Scalpels
• All-glass syringes
• Swabs
• Pharmaceutical products such as
• Liquid paraffin
• Dusting powder
• Fats and greaseA holding period of 1600
C for one hour is
employedHow to operate Working of hot air oven:
• Materials to be sterilised is kept inside the
oven
• Then adjust temperature control to the
temperature of 1600
C
• Close the doors and switch on the
machineThe total processing time of a hot air oven
consists of three periods:
• The heating up period: which is the time it
takes the materials to heat up to the
required temperature.Apx. 1hr
• Holding periods: which is the time at
which sterilisation is taking place at a
known temperature e.g. 1600
C for one
hour or 1500
C for 2 hours
• The cooling down time: The temperature
should be allowed to cool down by itself
and this may takes about 2 hours.
What are the advantages and disadvantages of hot air oven?
Advantages: It is an effective method of
sterilization of heat stable articles.
• The articles remain dry after sterilization
• This is the only method of sterilizing oils
and powders
• Disadvantages:
• Since air is poor conductor of heat, hot air
has poor penetration
• Cotton wool and paper may get slightly
charred
• Glasses may become smoky
• Takes longer time compared to autoclave
What is an autoclave? Explain the Structure, working and principle of Autoclaves
A strong, pressurized,Steam heated vessel
for Sterilization or cookingPrinciple:
• Water boils when its vapour pressure
(pressure exerted by a vapour on the
surface of the liquid) equals that of
surrounding atmosphere
• Hence when pressure inside a closed
vessel increases, the temperature at
which water boils also increases
• Saturated steam thus produced has
penetrative power
• When steam comes into contact with a
cooler surface it condenses to waterGives up its latent heat (The quantity of
heat absorbed or released by a substance
undergoing a change of state) to that
surface
• Process continues till the temperature of
that surface is raised to that of steam
• This result in the denaturation and
coagulation of protein inside the
microorganism
• Usual holding time is 121 0C for 15
minutes at 15 PSISimple laboratory Autoclave:
• Consists of a vertical or horizontal
cylinder of gunmetal or stainless steel, in
a supporting sheet iron case
• Lid or door is fastened by crew clamps
• Made airtight by an asbestos washerAutoclave has on its lid or upper side:
• A discharge tap for air and steam
• A pressure gauge
• A safety valve
• Heating is by
gas or electricityProcedure:
❖ Sufficient water is put in the cylinder
❖ Material to be sterilized is placed on the
tray
❖ Autoclave is heated
❖ Lid is screwed tight
❖ Discharge tap is kept opened for some
time to remove air from the autoclaveSteam air mixture is allowed to escape
freely till all the air inside has been
displaced
❖ Then the discharge tap is closed
❖ Safety valve is adjusted to the required
pressure (15 PSI)
❖ Steam pressure rises inside
❖ When it reaches the desired set level, the
safety valve opensThe excess steam escapes to maintain the
required pressure
❖ From this point, the holding period is
calculated
❖ When the holding period is over, the heater
is turned off
❖ Autoclave allowed to cool till the pressure
gauge indicates that the pressure inside is
equal to the atmospheric pressure
❖ The discharge tap is opened slowly and air
is let into the autoclave
What are the precaution we have to take while operating an autoclave
Articles should not be tightly packed
• The autoclave must not be overloaded
• Air discharge must be complete and
there should not be any residual air
trapped inside
• Caps of bottles and flasks should not be
tight
• Articles must be wrapped in paper to
prevent drenching (Wet thorougly).
• Bottles must not be overfilled.If the tap is opened when the pressure inside
If the tap is opened when the pressure inside
is high:
Liquid media will tend to boil violently Spill from their containers
If opened after the pressure inside has fallen below atmospheric pressure:
Excessive amount of water would have evaporated and lost from the media
