DISINFECTION

Dr Arun R
History
 Semmelwies (1818-1865)- demonstrated the
value of hand washing with antiseptic
solutions.
 Lister (1827-1912)- successful in reducing
wound infections by prophylactic application
of carbolic acid to wounds.
Disinfectant (important for exam)
 Usually a chemical agent (but some times a
physical agent) that destroys disease causing
pathogens or other harmful microorganisms,
but might not kill bacterial spores.
 Refers to substances applied to inanimate
objects.
Disinfection (important for exam)
 Thermal or chemical destruction of pathogens
and other types of micro organisms.
 It is less lethal than sterilization, because it
destroys most recognised pathogenic
microorganisms but not necessarily all
microbial forms.
Sterilization
 Validated process used to render a product
free of all forms of viable microorganisms
including bacterial spores.
 Sterilizer is the apparatus used to sterilize
medical devices, equipments or supplies by
direct exposure to the sterilizing agent.
Antiseptic
 Substance that prevents or arrest the growth
or action of micro organisms by inhibiting their
activity or by destroying them.
 The term is especially used for preparations
applied topically on living tissue.
Asepsis
 Prevention of contact with microorganism.
Sanitizer
 Agent that reduces the number of bacterial
contaminants to safe levels as judged by
public health requirements.
 Commonly used with substances applied to
inanimate objects.
Sterile
 State of being free from all microorganisms
Hospital disinfectant
 Disinfectant registered for use in hospitals,
clinics, dental offices or any other medical-
related facility.
 Efficacy is demonstrated against Salmonella
choleraesuis, Staphylococcus aureus and
pseudomonas aeruginosa.
Germicide
 Agent that destroys microorganisms,
especially pathogenic organisms.
Detergent
 Surface cleaning agent that makes no
antimicrobial claims on the label.
 They comprise a hydrophilic component and a
lipophilic component.
 Acts by lowering surface tension.
Cleaning
 Removal, usually with a detergent and water or
enzyme cleaner and water of adherent visible
soil, blood, protein substances, microorganisms
and other debris from the surfaces, crevices,
serrations, joints and lumens of instruments,
devices and equipment by a manual or
mechanical process that prepares the items for
safe handling and/or further decontamination.
Deodorant
 Deodorant is a substance which suppresses or
neutralises bad odours, eg, lime and
bleaching powder.
Properties of ideal disinfectant

1. Broad spectrum 8. Odourless

2. Fast acting 9. Economical
3. Not affected by 10. Solubility
environmental factors 11. Stability
4. Nontoxic 12. Cleaner
5. Surface compatibility 13. Environmentally friendly
6. Residual effect on treated
surfaces
7. Easy to use with clear
label directions
Types of disinfection (important for exam)
Concurrent disinfection

Terminal disinfection

Precurrent (prophylactic) disinfection

Concurrent disinfection (important for exam)
 It is the application of disinfective measures as soon
as possible after the discharge of infectious material
from the body of an infected person, or after the
soiling of articles with such infectious discharges.
 Disease agent is destroyed as soon as it is released
from the body.
 Consists of disinfection of urine, faeces, vomit,
contaminated linen, clothes, hands, dressings, aprons
gloves etc.
Terminal disinfection (important for exam)
 It is the application of disinfective measures after
the patient has been removed by death or to a
hospital or ceased to be a source of infection or
after other hospital isolation practices have been
discontinued.
 Now scarcely practiced.
 Terminal cleaning is considered adequate along
with airing and sunning of rooms, furniture and
bedding.
 Precurrent(prophylactic) disinfection
(important for exam)
 Disinfection of water by chlorine,
pasteurization of milk and hand washing are
examples of precurrent disinfection.
Disinfective agents (important for exam)
Natural agents

Physical agents

Chemical agents
Natural agents
1. Sunlight
2. Air
Sunlight
 Direct, continuous exposure- destructive to
many
 Ultra violet rays- lethal to bacteria and some
viruses
 Linen, bedding, furniture- disinfected by
exposure to direct sunlight for several hours.
Air
 Acts by drying or evaporation of moisture.
Physical agents
1. Burning
2. Hot air
3. Boiling
4. Autoclaving
5. Radiation
Burning
For inexpensive articles like contaminated
dressings, rags and swabs.

Faeces can be disposed by burning

Should not be done in open air, best done

in an incinerator.
Hot air
Good for glassware, syringes, swabs, dressings, oils, and sharp
instruments.

Has no penetrating power- not suitable for bulky articles such as

mattresses.

Usually done in a hot air oven.

Temperature should be maintained at 160-180 degC for one hour to

kill spores.
Boiling
Boiling for 5-10 minutes (rolling boiling) will kill bacteria but not viruses and
spores.

To destruct spores the temperature should be maintained above 100 degC.

Suitable for small instruments, linen, rubber etc.

Addition of 1% soap and 0.3% washing soda enhances the effect of boiling.

Drawbacks- slow process, not suitable for thick beddings and woollen
materials.
Autoclaving
Sterilizers which operate at high temperature and pressure.

Works on the same principle as that of pressure cooker.

Two types- gravity displacement and high speed prevaccum

sterilizers.

Destroys all forms of life including spores.

Has greater penetrating powers than ordinary steam.

Attains temperature of 122 deg C under 15 lbs/sq inch.

Acts by giving off its latent heat.

Absolute sterility obtained over 135 deg C.

Most effective method for linen, dressings, gloves, syringes.

Not suitable for plastics and sharp instruments.

Radiation
❖ Ionizing radiation is increasingly used for-
bandages, dressings, catgut and surgical
instruments.
❖ Objects are placed in plastic bags before
radiation, and will remain sterile until opened.
❖ Has great penetrating power with little or no
heating effect.
❖ Most effective method, but very costly.
❖ Commercial methods are mainly carried out by
gamma radiation.
 Chemical agents
Phenol and related compounds

Quaternary ammonia compounds

Halogens and their compounds

Alcohols

Formaldehyde

Oxidizing agents

Metals and microbicides

Lime

Ethylene oxide

Miscellaneous inactivating agents

Phenol and related compounds
1. Phenol
2. Crude phenol
3. Cresol
4. Cresol emulsions
5. Chlorhexidine (hibitane)
6. Hexachlorphane
7. Dettol
Phenol
Pure phenol or carbolic acid is the
best known member of this group.

Pure phenol is not an effective

disinfectant

It is used as a standard to compare

the activity of disinfectants
Crude phenol
Phenol that is commonly used for disinfection is crude phenol.

Mixture of phenol and cresol; dark oily liquid.

Effective against gram positive and gram negative bacteria, viruses; but less
effective against spores and acid fast bacteria.

Effect is greatly weakened by dilution.

For faeces- above 10%; for mopping- 5%

Cresol
It is an excellent coal tar disinfectant.

3-10 times as powerful as phenol, but no more

toxic.

5-10% for faeces and urine.

It is an all purpose general disinfectant.

Cresol emulsions
Emulsified with soap is known as saponified
cresol.

Lysol, izal and cyllin are examples.

Lysol contains 50-60 % cresol

2% lysol – good for faeces.

Chlorhexidine (hibitane)
 One of the most useful skin antiseptics.
 Highly active against vegetative gram positive
organisms and moderately active against gram
positive microbes.
 Soluble in water and alcohol.
 Inactivated by soaps and detergents.
 0.5 % alcoholic or aqueous solution- effective
hand lotion.
 Creams and lotion containing 1% hibitane- for
burns and hand disinfection
Hexachlorphane

Highly active against gram positive organisms,

but less effective against gram negative.

Slow in action, but shows cumulative effect on

skin and compatible with soaps.
Dettol

Chloroxylenol. (very important)

Relatively non toxic antiseptic and can be

used safely in high concentrations.

More easily inactivated by organic matter

than many other phenolic disinfectants.
Active against streptococci, but worthless
against some gram negative bacteria.

5% is suitable for disinfection of instruments and

plastic equipment- with contact time 15 minutes.
Quaternary ammonia compounds
1. Cetrimide
2. Savlon
Cetrimide
 Manufactured under the trade name
“cetavlon”.
 Highly active against gram positive and less
active against gram negative.
 Soluble in water
 Used as 1-2 % solution.
Savlon
 Combination of cetavlon and hibitane.(important)
 Plastic appliances – keeping in normal
strength savlon for 20 mins.
 1 in 6 in spirit is more effective than 1 in 20 in
aqueous solution.
 Clinical thermometers- 1in 6 spirit in under 3
minutes.
Halogens and their compounds
1. Chlorine and chlorine compounds
2. Iodine
Chlorine and chlorine compounds
1. Bleaching powder
2. Hypochlorites
3. Chlorine tablets
4. Alternative compounds that release chlorine
5. Superoxidised water.
Bleaching powder
 Chlorinated lime- (CaOCl2).
 White amorphous powder with a pungent smell of
chlorine.
 Good sample of bleaching powder contains about 33%
of “available chlorine”.
 Kills most of the microorganisms when used in 1 to 3 %.
 Widely used in public health practice in India- for
disinfection of water, faeces and urine; and as a
deodorant.
 The chief draw back is it is an unstable
compound and loses its chlorine content
on storage.
 5% solution is suitable for disinfection of
urine and faeces with a contact period of 1
hour.
Hypochlorites
 Most widely used chlorine disinfectant,
available as liquid or solid.
 Most prevalent chlorine products are aqueous
solution of 5.25 to 6.15 % of sodium
hypochlorite, usually called household bleach.
 Broad spectrum of antimicrobial activity
 Do not leave toxic residues, unaffected by
water hardness.
 Inexpensive and fast acting, remove dried or
fixed organisms and biofilms from surfaces.
Chlorine tablets
 Quite good in disinfecting small quantities of
water .
Alternative compounds that release chlorine

 Chlorine dioxide, sodium dichloro-iso-

cyanurate, chloramine –T.
 Retain chlorine more than hypochlorites; more
prolonged bactericidal effect.
Superoxidised water
 Saline is electrolysed to create a disinfectant
or antiseptic.
 Main products of this water are hypochlorus
acid and chlorine.
Iodine
1. Iodine solutions or tinctures
2. Iodophores
Iodine solutions or tinctures
 Have been used for a long time by health care
professionals as antiseptic for skin.
 It is bactericidal, fungicidal, virucidal and lethal
to spore bearing organisms.
 Cheap, readily available and quick in action.
Iodophores
 Combination of iodine and solubilizing agent or
carrier.
 Resultant complex- sustained release
reservoir of iodine and releases small amount
of free iodine in aqueous solution.
 Povidone iodine (betadine)- best known and
mostly used among iodophores.(important)
 Non irritant and do not stain the skin.
 Used for disinfecting blood culture bottles and
medical equipment.
Alcohols
 Ethyl alcohol and isopropyl alcohol are used
commonly.
 Ethyl alcohol- in the form of industrial methylated
spirit, used for skin disinfection and hand washing.
 Pure alcohol has no powers of disinfection, diluted
with water to 60-90 % vol/vol it is potent
bactericidal, virucidal, fungicidal and
tuberculocidal.
 Does not destroy bacterial spores.
 Activity decreases rapidly below 50%.
 70% is lethal for period of seconds to all types of
non sporing bacteria, but when applied on skin
and surfaces, its activity decreases on drying.
 Due to expense and inflammability- use is
restricted to small article disinfection.
 Most effective skin antiseptics are alcoholic
solutions of hibitane and iodine.
Formaldehyde
 Highly toxic and irritant gas, precipitates and
destroy protein.
 Commonly known in solution, as formalin.
 Effective against vegetative bacteria, fungi,
many viruses, but slowly effective against
bacterial spores and acid fast bacteria.
 Does not injure fabrics and metals.
 2-3 % solution- for spraying rooms, walls and
furniture.
 Formaldehyde gas – for disinfection of rooms;
blankets, beds, books and other articles which
cannot be boiled.
 Most effective at high temperature and at a
relative humidity of 80-90%
Oxidising agents
1. Potassium permanganate
2. Hydrogen peroxide
3. Paracetic acid
Potassium permanganate
 Used to disinfect aquariums and also widely in
community swimming pools to disinfect feet of
one before entering the swimming pool.
 Also used to disinfect fruits and vegetables.
Hydrogen peroxide
 Bactericidal, virucidal, sporicidal and fungicidal.
 Used in hospital setting to disinfect surfaces.
 Used as solution alone or with other chemicals as a
high level disinfectant.
 0.5% accelerated hydrogen peroxide – bactericidal
and virucidal – 1 minute; mycobactericidal and
fungicidal -5 minute.
 3% solution- antiseptic and for cleaning wounds and
discharging ulcers.
Paracetic acid
 Produced by reacting hydrogen peroxide with acetic
acid.
 Broadly effective against microorganisms; not
deactivated by catalase and peroxidase.
 Inactivates gram positive and negative bacteria, fungi
and yeast in less than 5minute and less than 100
ppm.
 Organic matter- 200-250ppm
 Viruses- 12-2250 ppm
Metals as microbicides
 Anti infective activity of heavy metals – known
since antiquity.
 Silver- prophylaxis of conjunctivitis of the new
born, topical therapy for burn wounds and bonding
to indwelling catheters.
 Zeolite ceramic coating containing silver and zinc
ions- inactivation of bacteria on stainless steal
surfaces.
 Silver, iron, copper- environmental control,
disinfection of water or reusable medial
devices or incorporated into medical devices.
Lime
 Cheapest of all disinfectants.
 Used in the form of fresh quick lime or 10-20%
aqueous suspension known as “milk of lime”.
 Faeces and urine- 10-20% aqueous suspension;
contact time-2 hours.
 Lime wash- used for treating walls.
 As a deodorant- sprinkled in cattle sheds and stables
and in public places where urinals and latrines are
located.
Ethylene oxide
 Kills bacteria, spores and viruses.
 Suitable for heat sensitive articles; sterilizes at
55-60 deg C.
 Ethylene oxide is explosive; mixed with carbon
dioxide.
 Water vapour increases the efficiency of
ethylene oxide.
 Good for Fabrics, plastic equipment, cardiac
catheters, books etc; but the process is difficult
to control.
Miscellaneous disinfectants
1. Pasteurization
2. Microwave
3. Flushing and washer disinfectors
4. Ultra violet radiation
5. Ozone
Pasteurization
 Not a sterilization process.
 Purpose is to destroy all pathogenic
microorganisms.
 Does not destroy bacterial spores.
Microwave
 Radio frequency waves, usually used at 2450
MHz.
 Produce friction of water molecules in an
alternating electrical field; friction generates heat.
 Microwaves produced by a home type microwave
oven (2.45 GHz) completely inactivate bacterial
cultures, mycobacteria viruses etc within 60
seconds to 5 minutes.
 Used in medicine for disinfection of soft
contact lenses, dental instruments, dentures,
milk, urinal catheters for intermittent self
catheterization.
Flushing and washing disinfectors
 Automated and closed equipment that clean
and disinfect objects from bed pans, urinals
and washbowls to surgical instruments and
anaesthesia tubes.
 Have short cycles of few minutes.
 Clean- by flushing with warm water, possibly
with a detergent.
 Disinfect- by flushing with hot water or with
steam.
 It empties, cleans and disinfects- manual
cleaning is eliminated, fewer disposable items
are needed, fewer chemical germicides are
used.
Ultra violet radiation
 Wavelength ranges from 328-210 nm.
 Maximum bactericidal effect occurs at 240-280
nm.
 Employed in the disinfection of drinking water,
air, titanium implants and contact lenses.
 Bacteria and viruses are more easily killed by
UV light than the bacterial spores.
Ozone
 Has been used for years as a drinking water
disinfectant.
 Powerful oxidant that destroys
microorganisms; but highly unstable.
Factors affecting the efficacy of sterilization
 While sterilizing the medical equipment, Following
factors should be kept in mind
Sl no Factors Effect
1 Cleaning Failure to adequately clean instruments results in higher
bioburden, protein load, and salt concentration. These will
decrease sterilization efficacy.

2 Pathogen type Spore-forming organisms are most resistant to sterilization.

However, the contaminating microflora on surgical
instruments consists mainly of vegetative bacteria.
Sl Factors Effect
no
3 Biofilm accumulation Biofilm accumulation reduces efficacy of
sterilization by impairing exposure of the
sterilant to the microbial cell.
4 Lumen length and Increasing lumen length and decreasing lumen
lumen diameter diameter impairs sterilant penetration. May
require forced flow through lumen to achieve
sterilization.
Sl Factors Effect
no
5 Restricted flow Sterilant must come into contact with
microorganisms. Device designs that prevent
or inhibit this contact (e.g. sharp bends, blind
lumens} will decrease sterilization efficacy.
6 Device design and Materials used in construction may affect
construction compatibility with different sterilization
processes.