This document discusses various methods of sterilization and disinfection. It defines key terms like sterilization, disinfection, disinfectant, antiseptic and aseptic. The major physical methods of sterilization described are heat (dry and moist), filtration and radiation. The chemical methods discussed are alcohols, aldehydes, phenols, halogens, oxidizing agents, salts, surface active agents, dyes and gases. Specific sterilization techniques like autoclaving, hot air oven, tyndallization are explained in detail.
2. DEFINITIONS
STERILISATION:
A process by which an article surface or a medium is made free of all
micro organisms either in vegetative or spore form.
DISINFECTION:
It means the destruction of all pathogens or organisms capable of
producing infection but not necessarily spores.
DISINFECTANT:
Products used to kill microorganisms on inanimate objects and
surfaces. They are not necessarily sporicidal but may be sporostatic
inhibiting germination or growth.
3. ANTISEPTIC:
A product that destroys or inhibits the growth of micro organisms on
living tissues.
ASEPTIC:
Characterised by absence of pathogenic microbes.
6. B. Chemical methods:
Alcohols
Aldehydes
Phenols
Halogens
Oxidising agents
Salts
Surface active agents
Dyes
Gases
7. Physical method:
SUNLIGHT:
Direct sunlight is a natural method of sterilisation in water tanks rivers
and lakes.
Sunlight is germicidal due to combined effect of UV and heat rays.
HEAT:
MOST reliable and commonly employed method of sterilisation.
PRINCIPLE:
i. DRY HEAT kills the micro organism by denaturation of bacterial
protein and by oxidative damage.
ii. MOIST HEAT kills th microorganism by denaturation and
coagulation of its proteins.
8. DRY HEAT STERILISATION:
Methods:
•Red heat
•Flaming
•Incineration
•Hot air oven
RED HEAT:
Inoculating wires, tips of foeceps are held in the
flame of a bunsen burner till they become red hot.
FLAMING:
Glass slide, scalpels and mouth of culture tubes
are passed through bunsen flame with out allowing
them to become red hot.
9. INCINERATION:
Infected materials are reduced to ashes by
burning.
Soiled dressings, animal wastes,
bedding and pathological materials are
delt with in this method.
10. HOT AIR OVEN:
Most widely used sterilisation by dry heat.
It is electrically heated and fitted with a fan and a thermostat to
maintain the chamber air at a particular temperature
Temperature and time:160 ºC
for 2 hours.
Used for sterilization of:
•Glass wares- petridish, flask
•Surgical instruments-scalpels,
scissors
•Chemicals- paraffin, sulphonamides
11. Precautions
•It should not be over loaded
•Materials should be arranged in such a way that allows the circulation of
hot air.
•Materials to be sterilized should be perfectly dry.
•Test tubes, flasks should be fitted with cotton plugs.
•Petridishes and pipettes should be wrapped in paper
•Rubber materials or any inflammable materials should not be kept inside
the oven.
•The oven must be allowed to cool for two hours before opening the doors
since the glasswares may crack.
12. Sterilisation control:
•Spores of non toxic strains of Clostridium tetani are
kept inside the oven .
•These spores will be destroyed if the sterilisation is proper.
•Thermocouples may also be used.
•Browene’s tube with green spot is available. After proper sterilization a green
colour is produced.
13. GLASS BEADS STERILIZER :
•The media used are glass beads, molten metal and
salt.
•The temperature achieved is of 220oC.
•The method employs submersion of small instruments
such as Endodontic files, artery forceps, scissors and
burs, into the beads; and are sterilized in 10 seconds
provided they are clean.
•A warm-up time of at least 20 minutes to ensure
uniform temperatures in these sterilizers.
14. MOIST HEAT STERILISATION:
This method of sterilisation may be used at different temperatures as follows:
•At a temperaturebelow 100ºC
•At a temperature 100ºC
•At a temperature above 100ºC
16. AT TEMPERATURE BELOW 100ºC:
a) Pasteurisation of milk: two types of method holder
(63ºC for 30 minutes) and flash (72ºC for 20 seconds
followed by cooling quickly to 13ºC or lower) are used.
b) Inspissation: some culture media like LJ medium and
Loeffler’s serum slope are rendered sterile by heating at
80- 85ºC temperature of half an hour daily on three
consecutive days. This process of sterilisation is called
inspissation.
c) Vaccine bath: bacterial vaccines are
sterilised in special bath at 60ºC for one hour.
17. AT A TEMPERATURE AT 100ºC:
Boiling:
• Boiling for 10-30 minutes destroy most of the vegetative forms.
• This methods may be used if no other methods are available.
• Not suitable for instruments that are used for surgical procedures.
18. Steam sterilizer - at 100ºC for 90 minutes:
• Koch’s or Arnold’s steam sterilizer is usually used for media which are
decomposed at high temperature of autoclave.
• The articles are placed on a perforated tray to let the steam to pass
through.
• They are exposed to steam at atmospheric pressure for 90 minutes.
19. Tyndallisation:
• Steam at 100ºC for 20 minutes on three successive days is
used
• The principle is that the first exposure kills the vegetative
forms and in the intervals between heating the remaining
spores germinate into vegetative forms that are killed during
consecutive heating.
• It is used for sterilisation of egg, serum,and sugar.
20. AT TEMPERATURE ABOVE 100ºC: (under pressure)
Autoclave:
•At normal pressure water boils at 100ºC, when the pressure inside a
closed vessel increases the temperature at which water boils also
increases, this is the principle a pressure cooker and an Autoclave.
• Steam above 100ºC or a saturated steam has a better killing power than
dry heat.
21. •An autoclave kills bacteria by coagulating its proteins.
•Saturated steam can penetrate porous materials
easily.
•When steam comes in contact
with a cooler object
it liberates its latent heat to
that surface.
•The process continues till the
temperature
of the article is raised to that of
steam, and the condensed
water produces moist
conditions for killing the
microbes present.
22. Components of auoclave:
I. It consists of a vertical or a horizontal cylinder of gunmetal or
stainless steel in a supporting iron case.
II. The lid is fastened by screw clamps and rendered air tight by an
asbestos washer.
III. The lid bears a discharge tap for air and steam, a pressure gauge
and a safety valve.
IV. The steam circulates with in the jacket and is supplied under high
pressure to the inner chamber where materials are kept for
sterilisation.
23. Method:
•The cylinder is filled with water and the material to be sterilized is placed
on the tray. The lid is closed with the discharge tap open and the heater
is put on. Safety valve is adjusted to the required pressure.
•After boiling the steam and air is allowed to escape till all the air has
been displaced.
•The pressure rises inside and when it reaches
the desired set 15 lbs per square inch the safety
valve opens and the excess air escapes.
•From this point the same pressure is
maintained for 15 minutes which is called the
holding period.
•After this period the heating is stopped and the
autoclave is allowed to cool till the pressure
inside the autoclave is equal to the
atmosphereic pressure.
25. Used for:
•Steriling culture media, rubber materials, dressings etc.,
•Materials that cannot withstand high remperatures of hot air oven.
Precautions:
•Air must be allowed to escape from the chamber as the temperature of air
steam mixtures is lower than that of pure steam.
•Materials should be arranged in such a
manner as to ensure free circulation of
steam inside the chamber.
26. Sterlisation control:
•Thermocouple: it is to record the temperature by a
potentiometer.
•Bacterial spores: spores of Bacillus Stearothermophilus are
used to test the organism.
•An envelope containing spores are placed
in the chamber, spores get
destroyed if sterilisation are proper.
Chemical indicators:
•Browne’s tube contains red solution
that turns green when exposed to
temperature of 121ºC for 15 min.
•Browne’s test strip available
that contain a chemical indicator.
27. Autoclave tape: is an adhesive tape used in autoclaving
(heating under high pressure with steam to sterilize) to indicate
whether a specific temperature has been reached. Autoclave
tape works by changing color after exposure to temperatures
commonly used in sterilization processes, typically 121°C in a
steam autoclave
28. Filtration:this method is useful for substances that get damaged by heat process,
e.g. Sera, sugars, antibiotic solutions etc.
Uses:
•Seperation of toxins and bacteriophages in bacteria
•Purification of water
•Filter discs can retain organisms that can be
cultured later
Types:
Earthernware candles:
•These have been used widely for industrial
drinking purpose.
•They are made in the form of hollow candles.
•The liquid to be filtered is passed into the
candles
They are of two types
a. Diatomaceous earth filters eg, berkefeld
b. Unglazed porcelain filters eg, chamber land
29. Asbestos disc filters (seitz filters):
• These are made up of asbestos (magnisium silicate)
• The filter is supported by a metal mount, attached to a metal flask
through a silicone rubber bung
• They are discarded after use
Membrane filters:
•Made up of cellulose esters.
•They are used in water analysis sterility
testing and for preparation of solutions
for parentral use
•Nitrocellulose membrane filters are
used these filters are available in sizes
from 0.015-12µm
•The 0.22µm is commonly used
because the pore size is smaller than
that of bacteria
30. Sintered glass filters:
•These are prepared by fusing different glass particles that are finely
powdered
•They are available in different pore sizes
31. Radiation:
1. Ionising radiation:
• They include gamma (γ) rays, X- rays, and the cosmic rays.
• They have a high penetrating power and are highly lethal to cells
that include bacteria
• Gamma radiations are used for sterilisation of disposable plastic
syringes, swabs, culture plates, cannulas catheters etc,.
• This method is also known as cold sterilisation because there is no
appriciable increase in temperature
32. 2. Non ionising radiation:
• These include infrared and ultra violet radiation(UV)
• Infra red radiations are used for rapid mass sterilisation of
syringes and catheters.
• UV radiation of wavelength 240-280nm are bactericidal in
nature
• They denaturate bacterial proteins and interfere with DNA
replication.
• UV radiation is used for disinfecting enclosed areas such as
laboratory, inoculation hoods, and operation theatres.
• Most vegetative forms of bacteria are susceptable to UV
radiation but their spore forms are highly resistant.
33. Chemical sterilization:
If heat disinfection/sterilization is not suitable to use for
some objects, chemical disinfecton sterilization can be
considered, the chemicals used are
1. Alcohols
2. Aldehydes
3. Phenols
4. Halogens
5. Oxidising agents
6. Salts
7. Surface active agentss
8. Dyes
9. Gases
34. ALCOHOLS
• Act by denaturing bacterial proteins.
• Solutions of 70% ethanol are more effective
than higher concentrations, as the presence of
water speeds up the process of protein
denaturation.
• Frequently used for skin antisepsis prior to
needle puncture.
• Isopropyl alcohol is preferred as it is a
better fat solvent, more bactericidal and
less volatile. Used for disinfection of clinical
thermometer .
35. Aldehyde compounds:
Formaldehyde:
A broad-spectrum antimicrobial agent, used for disinfection,
has limited sporicidal activity.
Uses: preservation of tissue for histological examination, sterilise
bacterial vaccines, prepare toxoid from toxin, for killing bacterial
cultures and suspensions.
Glutaraldehyde:
It is a high level disinfectant
A solution of 2% glutaraldehyde (Cidex), requires immersion of 20
minutes for disinfection; and 6 to 10 hours of immersion for
sterilization.
Uses: for sterilisation of cystoscopes endoscopes and bronchoscope,
To steriliise of endotracheal tube, corrugated rubber
anaesthtictubes etc
36. PHENOLS:
•They are active ingredients in some
household disinfectants. They are also
found in some mouthwashes and in
disinfectant soap and handwashes.
Phenols are toxic to cats and newborn
humans
•Phenol is probably the oldest known disinfectant as it was first used by
Lister, when it was called carbolic acid. It is rather corrosive to the skin and
sometimes toxic.
•o-Phenylphenol is often used instead of phenol, since it is somewhat less
corrosive.
37. •Chlorhexidine is widely used used in wounds preoperative disinfection of
skin as bladder irrigant etc.
•Chloroxylenol is the principal ingredient in Dettol, a household disinfectant
and antiseptic.
•Amylmetacresol is found in Strepsils, a throat disinfectant.
38. Halogens: Chlorine and iodine are two commonly usd disinfectants.
Chlorine:
•They are used in water supplies and swimming pools , chlorine in the form of
bleaching powder sodium hypochlorite and chloramine are also used.
•The action of all chlorine compounds is due to the release of free chlorine.
39. IODOPHOR COMPOUNDS
• Many studies have shown, that, iodophor compounds are the
most effective antiseptics,. Iodine is complexed with organic surface-
active agents, such as, polyvinylpyrrolidone (Betadine, Isodine). Their
activity is dependent on the release of iodine from the complex.
• These compounds are effective against most bacteria, spores,
viruses, and fungi. These are the most commonly used surface
disinfectants along with hypochlorite.
40. Oxidising agents:
1. Hydrogen peroxide:
• Hydrogen peroxide is effective against most organisms.
• Mode of action is by liberation of free hydroxyl radicalon decomposition
of H2O2.
• These free radicals are active ingredients in the disinfection process.
• They are used to disinfect contact lenses, surgical prostheses etc.,
41. 2. Peracetic acid:
Peracetic acid is an oxidising agent. It is one of the high level
disinfectants
The end products of this agent are non toxic
42. Salts:
•Salts of heavy metals have toxic effect on bacteria
•Salts of copper silver and mercury are used as dis infectant.
•Merthiolate (sodium ethyl mercurysalicylate)is used in dilution of 1:10,000 for
preservation of sera.
Surface active agents:
Substances which alter energy relationships at interfaces producing reduction of
surface tension are called surfectants.
They are classified into:
•Cationic - bactericidal.
•Anionic - strong detergent property but weak antimicrobial properties.
•Nonionic
•Amphoteric- possess both cationic and anionic properties
43. Dyes:
•Two groups of dyes aniline dyes and acridine dyes have been ued
extensively as skin and wound antiseptics
•Both are bacteriostatic in high dilution but have low bactericidal action.
•Aniline dyes include crystal violet, brilliant green and malachite green.
•Acridine dyes include acriflavine, euflavine, proflavine and amicarine.
44. GASES:
Formaldehyde:
•They are employed for fumigation of operation theraters.
• The reaction generates a enormous amount of heat so a heat
resistant containers are used
•The doors should be sealed after fumigation for 48 hours
•Sterilization is achieved by condensation of gas on exposed
surfaces
45. Ethylene oxide:
• It is effective against all types of micro organisms including viruses
and spores.
• It is used for the sterilization of plastics,rubbers, respirators,
sutures,and dental equipments.
•This method is commercially used for the sterilization of disposable
syringes
46. Betapropiolactone:
•This is a condation product of ketane and formaldehyde
•Though it is a gas it has low penetrating power
•It has rapid action and used in 0.2 percent
•It is more effictive for fumigation than formaldehyde
•It has some carcinogenic properties and are used in inactivation of
vaccines
48. Spaulding in 1968 classified dental instruments into three categories depending
on the risk of transmitting infection.
1. Critical
2. Semi-critical
3. Non critical
49. Critical instruments:
These are instruments that penetrate soft tissues bone or blood stream.
They have greatest risk of transmitting infection
Examples:
Surgical instruments, forceps, scalpels, scalers and burs
50. Semi- critical:
These are instruments the t donot contact bone or
blood stream but contact mucous membrane.
Examples:
Mouth mirrors, reuseable impression trays, amalgam
condensers etc.,
51. Non- critical:
These are instruments that come in contact with intact skin
Examples:
Dental chair, pulse oxymeter, BP cuff, X-ray cone etc.,
52. Steps in sterilization at office:
1. Presoaking
2. Cleaning
3. Packaging
4. Sterilization
5. Handling sterile instruments
6. Storage
7. Distribution
The Occupational Safety and Health Administration (OSHA) says, “The
person handling the instruments through removal, cleaning, packaging
and sterilization needs to use heavy-duty gloves to help prevent injury
with sharp contaminated instruments.”
Presoaking:
Used instruments are commonly placed in an anti microbial solution as this
softens and loosens debris. After which they are cleaned
53. Cleaning:
Using mechanical means of instrument cleaning rather than hand scrubbing
should minimize handling of instruments.
•If procedures are used where hand
scrubbing is necessary, heavy-duty
(utility) gloves, mask, eyewear and gown
should always be worn.
•Scrub only one instrument at a time
while holding it low in the sink.
•Use of a system utilizing locked
cassettes eliminates the need to sort,
handle and hand scrub individual
instruments.
54. Ultrasonic cleaning devices:
•An ultrasonic cleaner uses sound waves, that are outside the human hearing
range to form oscillating bubbles, a process called cavitation.
•These bubbles act on debris to remove it from the instruments.
•The timer is activated for three to
six minutes for loose instruments
and ten to twenty minutes for
instrument in cassettes.
•While the ultrasonic device is
running, the lid or cover should be
kept on to reduce the release of
aerosol and spatter into the area
from the ultrasonic cleaner.
55. Instrument washers:
Instrument washers use high-velocity
hot water and a detergent to clean
instruments.
Widely used for decades in hospitals
and large facilities as part of the central
sterilization process, these devices have
recently become available for the dental
office.
These devices require personnel to
either place instruments in a basket or to
use instrument cassettes during the
cleaning and drying cycles.
56. Thermal disinfectors:
These devices may look like the instrument washers described above;
however, there is one important difference.
The high temperature of the water and chemical additives in these devices
cleans and disinfects the
instruments.
57. Packaging:
Packaging used for instruments and cassettes
prior to sterilization includes wrap, paper
pouches, plastic pouches, combination
paper/plastic pouches and nylon tubing.
Sterilization packaging is specifically designed to
allow penetration of heat, steam or vapour and
then to seal the sterilized instruments inside the
package for sterile storage .
Sterilization:
58. Handling sterile instruments:
•Items must be placed in a way that ensures proper circulation of the
Sterile instruments.
• Items are placed in such a way that the packaging is not damaged.
•It is very important that instruments are completely dry when stored as
dampness encourages growth of microorganisms and corrosion.
• UV chambers and formalin chambers are used now a days for storage of
instruments.
59.
60. •Hands are the most common way diseases are
transmitted.
•Proper hand washing ensures proper aseptic
treatment procedures.
HAND WASHING:
61. 1. Immunisation
2. Patient screening
3. Hand washing
4. Barrier technique
• Personal protective equipments
• Rubber dam and preprocedural rinsing
5. Needle and sharp instrument safety
6. Instrument sterilisation and disinfection
7. surface disinfection
8. Radiographic asepsis
9. Loboratory asepsis
10.Infectious dental waste management and disposal
STANDARD PRECAUTIONS
