2. OUTLINE
Introduction
Definitions
Principles of sterilization and disinfection
Mechanisms of sterilization and disinfection
Individual disinfection processes/
Clinical applications
Research
Summary/Conclusion
3. INTRODUCTION
Microorganisms are the agents of
contamination, infection, and decay.
Hence it becomes necessary to remove
them from materials and areas.
Early civilization practiced salting,
smoking, pickling and exposure to
sunlight .
4. Definitions
Sterilization: A process intended to remove or destroy
all viable forms of microbial life, including bacterial
spores.
5. Definitions
Disinfection: The destruction of pathogenic and other
kinds of microorganisms by physical and chemical
means.
Disinfection is a less lethal process than sterilization
because it destroys most recognized pathogenic
microorganisms, but not necessarily all microbial forms
such as bacterial spores.
8. Definitions
Sterilizer: An agent that destroys or eliminates all forms
of microbial life in the inanimate environment,
including all forms of vegetative bacteria, bacterial
spores, fungi, fungal spores, and viruses.
9. Definitions
Disinfectant: An agent that frees from infection, usually
a chemical agents but sometimes a physical one, such
as x-rays or ultraviolet light, that destroy disease or
other harmful microorganisms but may not kill bacterial
spores. It refers to substances applied to inanimate
objects.
10. Definitions
Antiseptics: An agent that opposes sepsis,
putrefaction, or decay by preventing or
arresting the growth of microorganisms.
Antiseptic products are applied on or in the
living body of humans or other animals.
Antibiotics: an organic chemical
substance produced by microorganisms
that has capacity in dilute solutions to
destroy or inhibit the growth of bacteria
or other microorganisms.
It is usually used as a chemitherapeutant and
must be low in toxicity while effective against
microorganisms.
11. Definitions
Sterilization: complete killing of all
forms of microorganisms, including
bacterial spores
Disinfection: killing or removing of
harmful vegetative microorganisms.
Disinfectant: chemical substance
used to achieve disinfection.
Antiseptic: disinfectant that can be
safely used on living tissues.
12. Sepsis: Comes from Greek for decay or putrid. Indicates bacterial
contamination.
Asepsis: Absence of significant contamination.
Aseptic techniques are used to prevent contamination of surgical
instruments, medical personnel, and the patient during surgery.
Aseptic techniques are also used to prevent bacterial contamination in food
industry.
13. Methods of Microbial Control
Microbial Control
Methods
Physical Agents Chemical Agents
Mechanical Removal
Methods
14. Physical Agents
Heat Radiation
Dry Moist
Incineration
Dry Oven
Steam Under
Pressure
Boiling Water/Hot Water
Pasteurization
Sterilization
Ionizing Non Ionizing
X Ray, Cathode,
Gamma
Disinfection
UV
Sterilization Disinfection
17. Mechanisms of sterilizers and disinfectants
Sterilizer
Moist and dry heat: protein denaturation,
enzyme inhibition, RNA and DNA breakdown
Ionizing radiations: single or double-strand
breakage in DNA
Disinfectants
Ultraviolet radiation: thymine dimers, various
photoproducts (5,6-dihydroxy-dihydrothymine,
TDHT, pyrimine-(6-4)-pyrimidone,…)
Chemical disinfectants: protein denaturation,
enzyme inhibition, breakdown of nucleic acids
18. Mode of action of (chemical) disinfectants
Adsorption on the microbes’ surface
Diffusion through the surface
Binding to the vulnerable sites (e.g. plasma membrane,
cytoplasmic proteins, nucleic acids, and so on)
Disruption of the vulnerable sites
Injury and death of the microbes
26. Surface structure of
bacterial endospores
Exosporium: a thin protein cover
Spore coat: layers of spore-specific
proteins
Cortex: loosely cross-linked peptidoglycan
Core: core cell wall, cytoplasmic
membrane, cytoplasm, nucleoid,
ribosomes, and others
Remarkable physical barrier against
sterilization and disinfection
Survive up to 150 oC with dry heat
Extremely resistant to ultraviolet, strong acid
and bases, and chemical disinfectants
27. Surface structure of
Giardia cysts
An inner membrane
A thick (0.3 µm) outer filamentous
portion
Filaments
7-20 nm in diameter
Protein and a unique carbohydrate (ß(1-3)-
N-acetyl-D-galactopyranosamine)
Strong interchain interaction and tightly
packed meshwork
Remarkable physical barrier against
most chemical disinfectants
28. Physical Methods of Sterilisation
Sterilisation By Dry Heat:
Hot Air Oven
• Kills by oxidation effects
•The oven utilizes dry heat to
sterilize articles
• Operated between 50oC to
250/300oC.
•A holding period of 160oC for 1 hr
is desirable.
• There is a thermostat controlling
the temperature.
•Double walled insulation keeps the
heat in and conserves energy,
29. Uses:
To sterilise Forceps, Scissors, Scalpels, Swabs.
Pharmaceuticals products like Liquid paraffin.
30. FLAMING
Inoculation loop or Wire, the
tip of Forceps and spatulas are
held in a bunsen flame till
they are red hot.
31. INCINERATION
This is an excellent method of
destroying materials such as
contaminated cloth and
pathological materials.
33. MOIST HEAT STERILISATION IS CARRIED OUT WITH
FOLLOWING METHODS
Temp below 100oC: “Pasteurisation”, Inspissator.
Temperature at 100oC: Boiling.
Steam at atmospheric pressure: Koch/Arnold’s
steamer.
Steam under pressure: Autoclave.
34. Pasteurisation
Process of killing of pathogens in the
milk but does not sterilize it .
Milk is heated at 63oC for 30 mins.
(HOLDER METHOD)
At 72oC for 15-20 Sec. Rapid cooling to
13oC
(FLASH PROCESS)
36. HOT WATER BATH
To inactivate non sporing bacteria for the preparation of
vaccines - Special vaccine bath at 60oC for one hour is
used
Serum or body fluids containing coagulable proteins can
be sterilized by heating for 1 hr at 56oC in a water bath
for several successive days.
38. INSPISSATOR
Sterilizes by heating at 80-85oC for half an hour for 3
successive days
Used to sterilize media such as Lowenstein-Jensen &
Loefller’s serum
39. TEMPERATURE AT 100OC
Boiling:
Kills vegetative forms of bacterial pathogens.
Hepatitis virus: Can survive up to 30 minutes of boiling.
Endospores: Can survive up to 20 hours or more of boiling
41. STEAM AT ATMOSPHERIC PRESSURE
Steam is generated using a steamer (Koch/ Arnold)
Consists of a Tin cabinet
Has a conical lid to enable the drainage of condensed
steam
Perforated tray above ensures materials are surrounded
by steam.
For routine sterilization exposure of 90 mins is used
42. For media containing sugar and gelatin exposure of 100oC for 20 min for 3
successive days is used
The process is termed as
Tyndallisation /Intermittent Sterilization
43. STEAM UNDER PRESSURE - AUTOCLAVE
Works on the principle of Steam under pressure
Invented by Charles Chamberland in 1879.
45. Autoclave consists of a vertical or a horizontal cylinder.
One end has an opening which is meant for keeping materials to be
sterilised.
The lid is provided with a Pressure gauge, to measure the pressure
A safety valve is present to permit the escape of steam from the chamber
46. Articles to be sterilised are placed in the basket
provided
Sterilisation is carried out under pressure at 121º for 15
mnts.
47. CHEMICAL AGENTS
Chemical agents act by
Protein coagulation
Disruption of the cell membrane
Removal of Sulphydryl groups
Substrate competition
48. ALCOHOLS
Ethanol /Isopropyl alcohol are frequently used
No action on spores
Concentration recommended 60-90% in water
Uses
Disinfection of clinical thermometer.
Disinfection of the skin – Venupuncture
49. ALDEHYDES
Formaldehyde & Glutaraldehyde are frequently used
Formaldehyde is bactericidal, sporicidal & has a lethal
effect on viruses.
Glutaraldehyde is effective against Tubercle bacilli,
fungi and viruses
50. USES
FORMALDEHYDE
To preserve anatomical specimens
Destroying Anthrax spores in hair and wool
10% Formalin+0.5% Sodium tetra borate is used to sterilise metal
instruments
51. USES
GLUTARALDEHYDE
Used to treat corrugated rubber
anesthetic tubes, Face masks, Plastic
endotracheal tubes, Metal instruments
and polythene tubing
52. HALOGENS
Iodine in aqueous and alcoholic solution has been used
widely as a skin disinfectant
Actively bactericidal with moderate against spores
Chlorine and its compounds have been used as
disinfectants in water supplies & swimming pools
53. PHENOLS
Obtained by distillation of coal tar
Phenols are powerful microbicidal substances
Phenolic derivatives have been widely used as
disinfectants for various purposes in hospitals
Eg: Lysol, cresol
54. USES
Various combinations are used in the
control of pyogenic cocci in surgical &
neonatal units in hospitals.
Aqueous solutions are used in treatment
of wounds
55. METALLIC SALTS
The salts of silver, copper and mercury are used as
disinfectants.
Act by coagulating proteins
Marked bacteriostatic, weak bactericidal and limited
fungicidal activity
61. Microbial control by filtration
Filtration helps to remove bacteria from heat labile liquids such as sera and
solutions of sugar, Antibiotics.
The following filters are used
Candle filters
Asbestos filters
Sintered glass filter
Membrane filters
62. MEMBRANE FILTERS
Made of cellulose esters or other polymers
Uses
Water purification & analysis
Sterilization & sterility testing
Preparation of solutions for parenteral use
63. Filtration
May be done under either negative or
positive pressure. Example ; membrane
filter made of cellulose acetate. Generally
removes most bacteria but viruses and
some small bacteria e.g. Chlamydia &
Mycoplasma may pass through. Thus
filtration does not technically sterilize
items but is adequate for circumstances
under which is used.
Main use: for heat labile substances e.g.
sera, antibiotics.
65. Non- Ionising radiation:
Electromagnetic rays with longer wavelength
Absorbed as heat
Can be considered as hot air sterilisation
Used in rapid mass sterilisation of prepacked Syringes and
catheters
Eg: UV rays
66. IONISING RADIATIONS
X- rays, gamma rays & cosmic rays.
High penetrative power
No appreciable increase in the temperature – COLD
STERILISATION
Sterilise plastics Syringes, catheters, grease fabrics
metal foils
67. ULTRASONIC AND SONIC VIBRATION
Bactericidal
Microorganisms vary in their sensitivity, hence
no practical value in sterilisation and
disinfection
69. Factors influencing activity of
disinfectants
1. Activity directly proportional to temperature.
2. Directly proportional to concentration up to a
point – optimum concentration. After this level
no advantage in further increases in concentration.
70. Factors influencing activity of
disinfectants
3. Disinfectants may be inactivated by :
Dirt
Organic matter : Proteins, Pus, Blood, Mucus and
Feces.
Non organic: Cork, Hard water and Some plastics.
4. Time : Disinfectants need time to work.
5. Range of Action : Disinfectants not
equally effective against the whole
spectrum of microbes. e.g. Chlorhexidine
less active against Gram negative bacteria
than Gram positive cocci.
Hypochlorites and Gluteraldehyde are more
active against hepatitis viruses than most
other disinfectants.
72. Important points
Any instrument or item used for sterile
body site should be sterile.
Any instrument or item used for non-
sterile sites can be disinfected.
Hand washing is crucially important to
prevent hospital acquired infection.
