I N F E C T I O N
D I S I N F E C T I O N
A N T I S E P T I C
- K A L P E S H
A pathological condition due to the growth
of microorganisms in host
Chain of Infection
Portal of Exit
Causative agents / Infectious agent:
A microbial organism with the ability to cause disease.
Reservoir / Sources:
A habitat within which microorganisms lives, grows and multiplies.
Portal of Exit:
A place of exit providing a way for a microorganism to leave the
Upper respiratory tract
Saliva from the oral cavity
Feces / diarrhoea from the bowel
Skin and mucous membranes
Discharges from infected skin lesions and
Mode Of Transmission:
Method of transfer by which the organism moves or is carried from
one place to another.
Transmission of Infection
Vector-borne (mechanical or biologic)
• Person-to-person contact
• Contact with soil or vegetation harboring infectious organisms.
• Spray with relatively large, short-range aerosols produced by
sneezing, coughing, or even talking.
• Droplet spread is classified as direct because transmission is by
direct spray over a few feet, before the droplets fall to the ground.
• Eg. Pertussis and meningococcal
Transfer of an infectious agent from a reservoir to a host by suspended
air particles, inanimate objects (vehicles), or animate intermediaries
• Occurs when infectious agents are carried by dust or droplet nuclei
suspended in air.
• Airborne dust → settles on surfaces → become resuspended by air
• Droplet nuclei: less than 5 microns in size.
• Droplets fall to the ground within a few feet
Droplet nuclei may remain suspended in the air for long periods of
time and may be blown over great distances.
• Biologic products (blood)
• Fomites: inanimate objects such as handkerchiefs, bedding, or
• Fleas and ticks
• Carry an infectious agent through mechanical means or may support
growth or changes in the agent.
Portal Of Entry:
An opening allowing the microorganism to enter the host.
Upper respiratory tract
inhalation (eg. influenza)
sexual contact (eg. Chlamydia)
ingestion (eg. gastroenteritis)
Skin and mucous membranes
open wound or punctures
Needlestick injury (eg. hepatitis B)
Tubes placed in body cavities
such as urinary catheters
A person who cannot resist a microorganism invading the body,
multiplying, and resulting in infection.
Susceptibility of a host depends on:
• Genetic or constitutional factors
• Specific immunity
The state of being free of living pathogenic microorganisms
Process by which an article, surface or medium is made free of all
living microbes either in vegetative or spore state.
Process of reducing or eliminating living pathogenic microorganisms
in or on materials, so they are no longer able to cause disease.
The agent used to achieve this state is called Disinfectant.
Chemical disinfectants which can be easily applied on skin or mucus
membrane to prevent infection by inhibiting the growth of pathogens
• BACTERICIDAL AGENTS:
Agents which are able to kill bacteria.
• BACTERIOSTATIC AGENTS:
Agents which inhibit the multiplication of bacteria but does not
necessarily kill them.
Process of rendering an article or area free of danger from
Various agents used in
Sterilization & Disinfection
Ethanol, isopropyl alcohol
Dry heat :
Hot air oven, Incineration, Flaming
Boiling, Pasteurization, tyndallisation,
Ionizing, Non Ionizing
Ethylene oxide, Formaldehyde, beta
Metallic salts and surface active agents
Physical Methods of Sterilisation
• Direct sunlight is a natural method of sterilization of water in
tanks, rivers and lakes.
• Direct sunlight has an active germicidal effect due to the
combined effect of ultraviolet and heat rays.
• 4/5th of the bacterial weight is due to water.
• Therefore drying in air has deleterious effect on many
• This is unreliable method, spores are unaffected by drying.
• Most reliable method of sterilization
• Dry heat: Oxidative damage & toxic effect of elevated levels of
• Moist heat: Denaturation & coagulation of proteins.
• Time required for sterilization: inversely proportional to temp.
3. Hot air oven
Wire, the tip of Forceps
and spatulas are held in
a bunsen flame till they
are red hot.
Combustion at high temp
This is an excellent method of destroying
materials such as contaminated cloths, dressings,
animal carcasses and pathological materials.
Plastics such as PVC & polythene sterilized by
Polystyrene emits dense black smoke on
HOT AIR OVEN
• The oven utilizes dry heat to sterilize
• Low penetrating power
• A holding period of 160 C for 1 hr is
• At 180 C cotton plugs get charred
• Cutting instruments used in surgery
sterilized at 150 C for 2 hrs
• Oven heated by electricity.
• Fan fitted for even distribution of air.
• There is a thermostat controlling the
• Double walled insulation keeps the
heat in and conserves energy.
Recommended temp & duration:
160ºC for at least 45 mins.
170ºC for at least 18 mins.
180ºC for at least 7.5 mins.
190ºC for at least 1.5 mins.
To sterilize Glassware, Forceps, Scissors, Scalpels, Swabs
Pharmaceuticals products like Liquid paraffin, dusting powder, fats
Clostridium tetani used as microbiological test
Paper strips impregnated with spores: inserted in suitable packs
Removed & inoculated into Thioglycolate broth
Incubated at 37ºC for 5 days
1. Temp below 100°C:
2. Temperature at 100°C:
Koch/Arnold’s steamer (Steam sterilizer)
3. Steam under pressure (above 100°C):
TEMPERATURE BELOW 100 C
Process of killing of pathogens in the milk but does not
sterilize it .
Milk is heated at 63 C for 30 mins. (Holder method) or at
72 C for 15-20 Sec. (Flash process)
Followed by rapid cooling to 13 C
Non-sporing bacteria destroyed
Coxiella burtenii heat resistant & survives Pasteurisation
To inactivate non sporing bacteria for the preparation of
vaccines - Special vaccine bath at 60 C for one hour is used
Serum or body fluids containing coagulable proteins can be
sterilized by heating for 1 hr at 56 C in a water bath for
several successive days.
Hot water bath
Sterilizes by heating at 80-85 C for half an hour for 3
Media such as Lowenstein-Jensen & Loefller’s serum
sterilized in Inspissator.
Non-sporing bacteria killed by moist heat at 60 C for 30 mins
Temp of 80 C for 5-10 mins destroy vegetative forms of
bacteria, yeasts & moulds
Viruses inactivated rapidly at 60 C
TEMPERATURE AT 100 C
Kills vegetative forms of bacterial pathogens at 90-100 C.
Process hastened by adding 2% Sodium bicarbonate.
Not recommended for sterilization of surgical instruments
Sporing bacteria exposed for prolonged period.
Hepatitis virus: Can survive up to 30 minutes of boiling.
Endospores: Can survive up to 20 hours or more of boiling
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 water: ensures materials are surrounded by
For routine sterilization exposure of 90 mins is used
For media containing sugar and gelatin exposure of
100 C for 20 min for 3 successive days is used
Process is also termed as Intermittent Sterilization
- 1st exposure kills vegetative bacteria
- In intervals spores germinate into vegetative cells
which are killed on subsequent heating
STEAM UNDER PRESSURE
Steam under pressure (above 100 C)
has better killing power as compared to
dry heat: better penetration power
Bacteria more susceptible to moist
heat: bacterial protein coagulates
Steam coming in contact with cooler
surfaces condenses to water &
liberates latent heat to that surface
Autoclave consists of a vertical or a horizontal
cylinder. (Gunmetal or stainless steel in supporting
Lid: fastened by screw clamps
The lid is provided with:
Discharge tap: for air & steam
Pressure gauge: to measure the pressure
A safety valve is present to permit the escape of
steam from the chamber
Sufficient water added
Articles to be sterilised are placed on tray & autoclave is
Lid screwed tight with discharge tap open
When no more air comes out, discharge tap is closed
Sterilisation can be carried out under following conditions:
121 C for 15 mins.
126 C for 10 mins.
134 C for 3 mins.
Heater turned off & autoclave allowed to cool
Discharge tap opened to allow the entry of air in autoclave
Spores of Bacillus stearothermophilus used as test organism
Spores get killed on exposure of 12 mins at 121 C
Spores impregnated on paper strips: packed in envelopes →
inserted in different parts of autoclave → Sterilization →
inoculated into suitable medium → incubated
Records temp directly by potentiometer
3. Chemical indicators
Filtration helps to remove bacteria from heat labile liquids such as
serum and solutions of sugar, Antibiotics.
• To sterilize serum and solutions of sugar, Antibiotics for preparation
of culture media
• To obtain bacteria-free filtrates of clinical samples for virus isolation
• Separation of Toxins & bacteriophages from bacteria
• Filter discs to retain bacterial cells from liquid
• Candle filters
• Asbestos filters
• Sintered glass filters
• Membrane filters
Widely used for purification of
water for Industrial & drinking
1. Unglazed ceramic filter:
Eg. Chamberland filter & Doulton
2. Diatomaceous earth filters:
Eg. Berkefeld filter & Mandler
SINTERED GLASS FILTER
Prepared by heat fusing powdered
glass particles of graded size
Low absorptive property & can be
Made of cellulose esters or other
Water purification & analysis
Sterilization & sterility testing
Preparation of solutions for
1. Non-ionising: IR, UV
2. Ionising: Gamma, high energy electrons
Non- Ionising radiation:
• Electromagnetic rays with longer wavelength
• Absorbed as heat
• Infrared rays: Can be considered as hot air sterilisation
• IR: rapid mass sterilisation of prepacked Syringes and catheters
• UV: disinfecting enclosed areas like operation theatres, laboratories
X- rays, gamma rays & cosmic rays.
Lethal to DNA & other vital constituents
High penetrative power
No appreciable increase in the temperature – Cold sterilisation
Sterilise plastics Syringes, swabs, catheters, animal feed, grease,
fabrics, metal foils
Ultrasonic & Sonic Vibrations
Microorganisms vary in their sensitivity, hence no practical value
in sterilisation and disinfection
Chemicals can be used as Antiseptics & Disinfectants
Potency of disinfectants depends on:
Concentration of substance
Time of action
pH of medium
Nature of organism
Presence of extraneous material
Characteristics of Ideal Antiseptic or Disinfectant:
Wide spectrum of activity (effective against all microbes)
Active in presence of organic matter
Effective in acid or alkaline media
High penetrating power
Should not lead to corrosion of metals
Should not cause local irritation
No interference with healing
Should not be toxic if absorbed into circulation
Inexpensive & easily available & easy to use
Chemical agents act in one of the following ways:
Disruption of the cell membrane
Removal of free Sulphydryl groups (required for enzyme
Substrate competition: compound resembling essential
Ethanol /Isopropyl alcohol are frequently used
As skin antiseptics: denature proteins
No action on spores
Concentration recommended 60-90% in water
Isopropyl alcohol preferred: better fat solvent, more bactericidal,
Disinfection of clinical thermometer.
Methanol: effective against fungal spores → Used for treating
cabinets & incubators
Formaldehyde & Glutaraldehyde are frequently used
Bactericidal, sporicidal & has a lethal effect on viruses
Used to preserve anatomical specimens
Destroying Anthrax spores in hair and wool
10% Formalin+0.5% Sodium tetraborate is used to sterilise metal
Formaldehyde gas: irritant & toxic when inhaled
used for sterilizing instruments & heat-sensitive catheters,
fumigating wards, laboratories
Action similar to formaldehyde
Effective against Tubercle bacilli, fungi & viruses
Less irritant & toxic to eyes & skin
Used to treat corrugated rubber anesthetic tubes, Face masks,
Plastic endotracheal tubes, Metal instruments and polythene tubing
Bacteriostatic in nature
Are Brilliant green, Malachite green & Crystal violet
Active against Gram positive bacteria
No activity against tubercle bacilli. Hence, malachite green used in
Non-toxic & non-irritant to tissue but inhibited by organic material
Impair the DNA complexes in bacterial cell
Effective against Gram positive
Important dyes are Proflavine, Acriflavine, Euflavine, Aminacrine
Iodine in aqueous and alcoholic solution has been used widely
as a skin disinfectant
Actively bactericidal with moderate action against spores
Active against Tubercle bacilli & viruses
Chlorine and its compounds have been used as disinfectants in
water supplies, swimming pools, food & dairy industries
Used commonly as hypochlorites (ClO)
Wide spectrum of action against viruses
Obtained by distillation of coal tar at 170-270 C
Damage cell membrane releasing cell contents
Phenolic derivatives have been widely used as disinfectants for
various purposes in hospitals
Lysol, cresol: active against wide range, not inactivated by organic
matter, but toxic to humans
Hexachlorophene: toxic, should be handled with care
Chlorhexidine: non-toxic antiseptic, most active against Gram +ve
Various combinations are used in the control of pyogenic cocci in
surgical & neonatal units in hospitals.
Aqueous solutions are used in treatment of wounds
Colourless, Highly penetrating gas with a sweet ethereal smell.
Effective against all types of microorganisms including viruses and
Inflammable & explosive at high concentration
Alkylate carboxyl, hydroxyl & amino group in protein and also
react with RNA & DNA
Toxic, mutagenic & carcinogenic
Specially used for sterilising heart-lung machines, respirators,
sutures, dental equipments, books and clothing.
Also used to sterilise Glass, metal and paper surfaces, plastics, soil,
some foods and tobacco.
Widely employed for fumigation of operation theatres and other
When formaldehyde vapour is generated, doors should be sealed &
left unopened for 48 hrs
Beta Propiolactone (BPL):
Low penetrating power but more efficient than formaldehyde for
Used in fumigation
For sterilisation 0.2% BPL is used
Has a rapid biocidal activity, but carcinogenic
Very effective against viruses
SURFACE ACTIVE AGENTS & METALLIC SALTS
Surface active agents:
Substances which reduce the surface tension
Used as wetting agents, detergents & emulsifiers
Classified as: Anionic, Cationic, Nonionic & Amphoteric
Cationic compounds act on PO4 group in cell membrane
Cations are widely used in the form of quaternary ammonium
Markedly bactericidal, active against Gram positive organisms.
No action on spores, tubercle bacilli, viruses
Anionic compounds (soaps): moderate action
Soaps from saturated fatty acids: against Gram –ve
Soaps from unsaturated fatty acids: against Gram +ve
Salts of heavy metals: greater action
The salts of silver, copper and mercury are used as disinfectants.
Act by coagulating proteins
Organic compounds: marked bacteriostatic, weak bactericidal and
limited fungicidal activity
Mercuric chloride: highly toxic
Copper salts: fungicides
TESTING OF DISINFECTANATS
Activity of disinfectant to be tested is compared to the activity of
phenol of varying concentration
Disinfectant is tested in the presence of organic matter