STERILIZATION AND DISINFECTION BY DR. PRASHANT PATIL

1. STERILIZATION &
DISINFECTION
Dr Prashant Patil
PROFESSOR AND HEAD
ORAL MEDICINE AND RADIOLOGY
NAVODAYA DENTAL COLLEGE

2. •Microorganisms are ubiquitous.
•They cause contamination, infection and decay.
•So it is necessary to remove them from materials and areas. This
is the objective of sterilization
Health care professionals must learn and practice infection control
techniques that limits the spread of contagions .
violate an epithelial surface
Contaminated with patient blood and saliva

3. DEFINITIONS
 Sterilization-The process by which an article , surface or medium
is freed of all living micro-organism either in the vegetative or
spore state.
 Disinfection- the process of the destruction or removal of all
pathogenic organisms , or organisms capable of giving rise to
infection.

4.  Disinfectants- A chemical agent used on inanimate
objects to kill vegetative microorganisms, viruses and
fungi, but not necessarily bacterial endospores.

5.  Antisepsis- Prevention of infection usually by inhibiting
the growth of bacteria is called antisepsis
 Antiseptics- Chemical disinfectants which can be safely
applied to the living tissues and are used to prevent
infection by inhibiting the growth of bacteria

6. HISTORY
 .
Semmelweis introduced the concept of hand washing
with lime
Florence  Later laid down the principles of proper
hygiene and nursing procedures
Lister  Introduced the concept of antiseptic surgeries
using carbolic acid
Louis Pasteur  Put forth the concept of
sterilization techniques using hot air oven, autoclave
and sterilizers

7. CLASSIFICATION OF STERILIZATION METHODS
Physical
agents
Sunlight
Dry heat
Moist
heat
Filtration
Radiation
Ozone
Alcohol
Aldehydes
Dyes
Halogens
Phenols
Surface active agents
Gases
Oxidising agents
Salts
CHEMICAL
AGENTS

8. PHYSICAL AGENTS
1.Sunlight :
 Bactericidal activity.
 Germicidal activity because of U
V rays + heat.
 Water in tanks, rivers & lakes.
 Studies have shown that in India,
typhoid bacilli exposed to sun on
pieces of white drill cloth were
killed in 2 hours where as
controls kept in dark room were
still alive after 6 days.

9. 2.Heat
a. Dry heat
b. Moist heat
FACTORS
AFFECTING
STERILIZATION
BY HEAT
Time and
temperature
Nature of heat
Type of material
Characteristics
of organism
No of
microorganisms
present
Heat is the most reliable method of sterilization, and
should be the method of choice unless
contraindicated

10. DRY HEAT
4 methods of dry sterilization:
1. Red Heat
2. Flaming
3. Incineration
4. Hot air oven

11. Red Heat
• Inoculating wires or loops, tips of forceps and needles
are held in the flame of a Bunsen burner till they
become red hot
Flaming
• Bunsen flame is used without allowing instrument or
object to become red hot.
• Uses: Scalpel blades, needles, mouth of culture tube,
glass slides and cover slides.

12.  Incineration
 Infective material is reduced to ashes by burning.
 Excellent method for destroying materials such as
soiled dressings, animal carcasses, bedding &
pathological materials .

13. HOT AIR OVEN
• Kills by oxidation effects
• Operated between 150oC to 250/300oC.
• There is a thermostat controlling the
temperature.
 Double walled insulation keeps the heat
in and conserves energy

14. Uses:
 To sterilize forceps, Scissors, Scalpels, Swabs ,
glasswares , petridishes, pipettes, test tubes and
flasks
 Pharmaceuticals products like Liquid paraffin,
dusting powder, fats and grease.

15. ADVANTAGES
Relative ease of use
Carbon steel instruments and burs do
not rust, corrode or lose their temper
or cutting edges if they are well dried
before processing
Rapid cycles are possible at high
temperatures
A number of time – temperature
combinations can be used

16. DISADVANTAGES
 High temperatures may damage more heat sensitive items such as
rubber or plastic items
 Sterilization cycles are prolonged at lower temperatures
 Cycles are not automatically timed on some models
 Inaccurate calibration, lack of attention to proper setting and adding
instruments without restarting the timings are common sources of error
MOIST HEAT
MOIST HEAT

17. MOIST HEAT
below
1000
centigrade
at 1000
centigrade
According to
the
temperature
above
1000
centigrade
Protein
denaturation
Coagulation
of protein
Action
Advantage of steam lies in the latent heat liberated when it
condenses on a cooler surface raising the temperature of that
surfaces.
1. Steam at atmospheric
pressure
2. Steam under pressure

18. TEMPERATURE BELOW 100 DEGREE CELSIUS
Pasteurization is a process of heating a food to a specific
temperature & time and then immediately cooling .
It aims to reduce the number of viable pathogens so
that they are unlikely to cause disease
a. 630C for 30min (Holder method)
b. 720C for 15-20 sec (Flash process ) following by
cooling quickly to 130C
The HTST pasteurization standard was designed to
achieve a five-log reduction, killing 99.999% of the
number of viable micro-organisms in milk.
This is considered adequate for destroying almost all
yeasts, molds, and heat-resistant organisms
(including Mycobacterium tuberculosis, but not
Coxiella burnetii

19. Vaccine bath  vaccine of non
sporing bacteria  are
sterilized at 600C for 1 hour.
Serum or body fluids containing
coagulable protein  sterilised
for 1 hour at 560 C
Inspissator  80 – 850C for 30min
Lowenstein Jensens and
Loeffer’s serum are rendered
sterile for 3 successive days in
an inspissator

20. Temperature at 1000C
 (Boiling)  (10 – 30 min)
 Vegetative bacteria are killed almost at 900C – 1000C but
sporing bacteria require considerable periods of boiling.
 Boiling is not recommended for surgical instruments.
 Hard water should not be used
2% NaH CO3
 Hard water soft water
 Lid should not be opened during this period.

21. Steam at atmospheric pressure 1000C :
 Used for sterilization of culture media which may
decompose if subjected to increase in
temperature.
 Koch or Arnold steamer is usually used.
 Steam at normal atmospheric pressure 1000C 
90 min.
 For media containing sugar or gelatin, exposure of
1000C for 20 min for 3 successive days is used –
this is known as.

22. Tyndallization or intermittent sterilization :
The principle is first exposure kills all gram –ve
bacteria and spores present will germinate in
favourable medium and are killed in subsequent
occasion.

23. Steam under pressure :
An autoclave is a
device used to sterilize
equipment and is
supplied by subjecting
them to high pressure &
saturated steam
The name comes from Greek auto-,
ultimately meaning self, and Latin
clavis meaning key—a self-locking
device
CHARLES
CHAMBERLAND

24. PRINCIPLE
 Water boils when its vapor pressure
equals that of the surrounding atmosphere
 When the pressure inside a closed vessel
increases, the temperature at which water
boils also increases.
 Saturated steam has greater penetrative
power.
 The large decrease in volume sucks in
more steam to the area and the process
continues
 The condensed water ensures moist
conditions for killing the microbes present.
 The energy that is instantly released when
steam comes into contact with an object
and quickly denatures vital cell proteins

25. ADVANTAGES
 It is the most rapid and effective method for sterilization of cloth, surgical
packs, and towel (other methods are not suitable for processing cloth
packs).
 Temperature can be accurately controlled
 Heating and penetration of the steam is rapid and effective
 Shortest sterilizing time (faster than dry heat, ethylene oxide and
chemical solution)
 Most effective sterilizing agent
 Relative availability of office proportioned autoclaving equipment

26. DISADVANTAGES
 No facility for drying the load after sterilization and before taking it out
 Method of air discharge is inefficient and it is difficult to decide when the
discharge is complete
 Items sensitive to the elevated temperature cannot be autoclaved .
 Tendency of moist heat to rust or dull instruments (tends to rust carbon
steel instruments) .
 Cost of autoclave .
 It takes seven times as much heat to convert boiling water to steam as it
takes to cause the same amount of water to boil at room temperature.

27. DRY HEAT VS MOIST HEAT
Sl.
no
Properties Dry heat Moist heat
1. Principal antimicrobial effect Oxidizes cell
protein
Denatures cell
proteins
2. Time to achieve sterilization Long Short
3. Equipment complexity and cost Low High
4. Tendency to dull or rust instruments Low High
5. Availability of equipment size for
office use
Good Good

28. FILTRATION
 This is the method used to remove bacteria from heat labile liquids
 Useful for antibiotic solutions, and carbohydrate solutions used in the
preparation of culture media.
 Various types of filters in use
1. Earthen Ware Candles – Berkfield , Chamberland
2. Asbestos Disc Filters – e.g. Seitz
3. Sintered Glass Filters
4. Membrane Filters

29. Membrane filters
 These are widely used now-a-
days.
 These are made up of
CELLULOSE ESTER
 The range of pore size in which
these are available is 0.05 –
12mm
Uses:
1. Water purification and analysis
2. Sterilization
3. Sterility testing
4. Preparations of solutions for
parenteral use
5. Isolation of virus & production of
bacteria free filtrate.

30. RADIATION
Ionizing radiation :
 X rays, gamma rays and cosmic rays are used.
 Lethal to DNA and other vital constituents of cell
 Penetrative power is high
 Uses: plastic items, syringes, swabs, catheters, animal
feeds, cardboard, oils, greases, fabrics and metal foils.
Non ionizing radiation:
 Infra red and ultraviolet rays are used.
 Uses: pre packed items such as syringes and
catheters.

31. ULTRASONIC AND SONIC VIBRATION
• It is high frequency sound waves.
• They are credited with bactericidal powers
• Microorganisms vary in their sensitivity to them
Causes their
destruction
As the bubble collapses , alternate
high and low pressure areas
impinge on microorganism
High frequency sound
waves cause formation
of microscopic bubbles
in fluid

32. CHEMICAL AGENTS
An ideal antiseptic or disinfectant should:
 Have wide spectrum of activity
 Be active in presence of organic matter
 Be effective in acid as well as alkaline medium
 Have speedy action
 Have high penetrating power
 Be stable
 Compatible with other antiseptics and disinfectants
 Not corrode metals
 Not cause local irritation or sensitization
 Not interfere with healing
 Not toxic if absorbed into circulation
 Be cheap and easily available
 Be safe and easy to use

33. Potency
Concentration
Time of
action
pH of the
medium
Temperature
Organisms
Main mode of action:
1. Protein coagulation
2. Disruption of cell membrane
3. Removal of free sulpydryl
groups for functioning of
enzymes
4. Substrate competetion : a
compound resembling the
essential substrate of enzyme
diverts or misleads it leading to
death

34. ALCOHOL
• Most commonly used are ETHYL
ALCOHOL and ISOPROPYL ALCOHOL.
• They act by denaturing bacterial proteins.
• They are mainly used as skin antiseptics.
• They have no action on spores and viruses.
• To be effective, the concentration used in
60% - 70% of water.

35. Formaldehyde
• It is effective against the
amino group in the protein
molecule.
• In aqueous solutions, it is
markedly bactericidal,
sporicidal and possess
lethal effect on viruses.
•Uses – To preserve
anatomical specimens.
To sterilize heat sensitive
catheters & clean metal
instruments. Percentage
used in 2% - 5%.
Gluteraldehyde
•Its action is similar to
formaldehyde.
•It is specially effective
against tubercle bacilli,
fungi and virus.
•It is used mainly to treat
corrugated rubber
anesthetic tubes, face
masks, plastic
endotrachealtubes, metal
instruments, respirators
ALDEHYDES

36. DYES
 Aniline dyes
 Acridine dyes
 Both are bacteriostatic in high dilution and are used as skin
and wound antiseptics.
 Aniline dyes has lethal effect on bacteria due to its action with
the acid groups in the cell.
 Acridine dye act by impairing the DNA complex of the
organism and thus kill or destroy the reproductive capacity of
the cell.
 Use – in lab as selective agents in culture media

37. PHENOLS
 Their lethal effect is due to their capacity to cause cell
membrane damage, thus releasing cell contents and causes
lysis.
 Agents are used
1. Carbolic acid – powerful microbicidal substance
2. Lysol & cresols – it is active against wide range of
organisms. Various proprietary preparations of phenols are
used (e.g.) chlorophenols, chloroxyphenols and their various
combinations are used. The commercial 4.8% solution of
choloroxylenol is known as dettol .

38.  Chlorhexidine (Hibitane) – it is a relatively non-
toxic skin antiseptic. Mostly active against gram
positive organisms and fairly active against gram
negative ones. It is effective in the presence of pus
or blood.

39. HALOGENS
Mainly used are iodine and chlorine
1. Iodine – it is a skin disinfectant in aqueous solutions and
alcoholic solutions and an active bactericidal agent.
Moderate action against spores. Normal percentage used is
5%.
2. Chlorine –used mainly in water supplies, swimming pools ,
food and dairy industries. Most commonly used as
hypochlorites. It is markedly bactericidal and active against
wide spectrum of viruses.

40. GASES
ETHYLENE OXIDE:
 It is highly lethal to all kinds of microbes including spores
and tubercle bacilli.
 Uses: plastic and rubber articles, blankets and
pharmaceuticals products.
 Ethylene oxide which is a gas at a B.P. of 10.8 degree
centigrade destroys organism by alkalization.
 Time – 10 – 16 hours depending on both the temperature
and the concentration of ethylene oxide used.

41. FORMALDEHYDE:
 used for fumigation of operation theatres and other rooms.
 Formaldehyde gas is generated by adding 150 grams of potassium
nitrate to 280ml formalin for every 1000 cubic feet of room volume.
 The reaction produces considerable heat, and so heat resistant
vessels should be used .
BETA PROPIOLACTONE :
 It has a rapid biocidal action but has carcinogenic activity.
 For sterilization of biological products 0.2% BPL is used.
 It kills all micro organisms and is very active against viruses.

42. SURFACE ACTIVE AGENTS
 These are substances which alter energy relationships at
interfaces producing a reduction of surface or interfacial
tension. They are widely used as wetting agents, detergents
and emulsifiers.

43. Classification
 Anionic (e.g.) common soap
 Cationic are the most important surface active antibacterial
agents. They act by denaturation of proteins.
The commonly used are
 Acetyl trimethyl ammonium bromide (cetavlon or cetrimide)
 Benzalkonium chloride
 Nonionic
 Amphoteric
 They are active against both gram positive and gram
negative organisms.

44. OXIDISING AGENTS
Hydrogen peroxide:
 It is used as a biocide for disinfection sterilization and antisepsis.
 Greater activity is seen against gram positive and gram negative
bacteria.
 It acts as an oxidant by producing hydroxyl free radicals, which attacks
essential cell components, including lipids, proteins and DNA.
 Concentration: it is ranging from 3 – 90 %

45. WASTE MANAGEMENT
 Biomedical waste:
The United Nations Conference on Environment & Development
(UNCED) in 1992 recommended the following measures :
1. Prevent & minimize waste production
2. Reuse or recycle the waste to the extent possible
3. Treat waste by safe & environmentally sound methods
4. Dispose off the final residue by landfill in confined and carefully
designed sites
Any waste generated during the diagnosis, treatment or
immunization of human beings or animals or in research
or in production or testing of biologicals

46. CATEGORIES OF BIOMEDICAL WASTE IN INDIA
Option Waste category Treatment disposal
Category 1 Human anatomical waste Incineration/ deep burial
Category 2 Animal waste Incineration/ deep burial
Category 3 Microbiology & biotechnology waste Autoclaving / microwave / incineration
Category 4 Waste sharps Disinfection chemical treatment
/autoclaving / microwaving /
mutilation/ shredding
Category 5 Discarded medicines & cytotoxic
drugs
Incineration, drug disposal in secured
landfills
Category 6 Solid waste( from blood , cotton
dressing , linen, bedding )
Incineration / autoclaving /
microwaving
Category 7 Solid waste ( tubings , catheters , IV
sets)
Disinfection chemical treatment ,
autoclaving/ microwaving / mutilation/
shredding
Category 8 Liquid waste Disinfection chemical treatment &
discharge into drains
Category 9 Incineration ash Disposal in landfill
Category 10 Chemicals used in disinfection Chemical treatment ( discharge &
land fill )

47. Colour Type of container Waste category Treatment option
Yellow Plastic bag Category 1, 2 and
Category 3, 6
Incineration/deep
burial
Red Disinfected
container/Plastic
bag
Category 3, 6, 7 Autoclaving/Microw
aving/ Chemical
Treatment
Blue/White
translucent
Plastic bag/punture
proof container
Category 4, 7 Autoclaving/Microw
aving Chemical
Treatment and
destruction/shreddi
ng
Black Plastic bag Category 5, 9 and
Category 10 (solid)
Disposal in
secured landfill