Sterilisation and disinfection

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STERILISATION
AND
DISINFECTION

Sterilisation
A process by which an article, surface or medium is
free of all living organisms either in vegetative state
or spore state
Disinfection
Removal or destruction of all pathogenic organisms
Asepsis
Prevention of infection by inhibiting the growth of
bacteria
STERILISATIO
N

Cleaning

Removal of soil and dirt to reduce microbial
burden and to make sterilisation more effective
Decontamination

The process of rendering an article or an area free
of contamination including microbial, chemical,
radioactive, etc.
Bactericidal agents: Agents that kill bacteria
Bacteriostatic agents: Agents that prevent
multiplication of bacteria
STERILISATIO
N

Objective: To destroy microorganisms from
materials and areas
Choice of method depends on: Purpose for which
it is carried out, nature of microorganisms, material to
be sterilised
Uses of sterilisation: To prevent contamination by
extraneous organisms, to prevent sepsis in surgery, for
safety in food and drugs
STERILISATIO
N

CLASSIFICATI
ON
Physical methods
Sunlight, drying, Heat
Dry heat - flaming- incineration, hot air oven
Moist heat- Pasteurisation, boiling
- Steam under normal pressure
- Steam under pressure
Filteration,
Radiation
Ultrasonic and sonic vibration

Chemical methods
Alcohols - Ethyl alcohol, isopropyl alcohol
Aldehydes - Formaldehyde, glutaraldehyde
Dyes
Halogens
Phenols
Surface active agents
Metallic salts
Gases: ETO, formaldehyde,betapropiolactone
CLASSIFICATI
ON

DRY HEAT

Drying
MoiMoisture is essential for the growth of bacteria.
Four fifths of weight is due to water.Hence drying
has a deleterious effect on bacteria but is not a
reliable method
Spores are unaffected by drying

FLAMING
• Flaming: Exposing the articles to be
sterilised to blue flame of the burner till it
becomes red hot.
• Inoculating loops, wires, tip of forceps,
scalpels,scissors and edges of test tubes,

Temperatures >1000c
Excellent method for destroying contaminated cloth,
animal carcasses, pathological materials, infectious
hospital waste
Plastics such as PVC and polythene can be dealt with
but polyesterine materials emits dense clouds of
black smoke
INCINERATION

Holding period – 160°C for 1 hour
- Glassware, instruments, liquid paraffin, dusting
powder, fats, grease, etc.
- Rubber, cotton avoided
Controls - C.tetani spores and Browne’s tubes
HOT AIR OVEN

HOT AIR OVEN
Hot air oven

STERILISATION CONTROL
Physical

Temperature monitoring and thermocouples
Chemical

Browne’s tube (green spot)
Biological

Non-toxigenic strain of Clostridium tetani or
Bacillus subtilis

Paper strips impregnated with 106
spores
inserted in pack to be sterilised

MOIST HEAT
Temp <100°C

Pasteurisation
– Holder method- 63°C – 30 min
– Flash method – 72°C – 20 sec
Followed by quickly cooling to 13°C

Vaccine bath: Heat inactivation – 60°C – 1 hr

Inspissation: 80–85°C 30 min on 3 days

Temperature at 100°C

Boiling

Koch & Arnold steam steriliser:
media –90 min

Tyndalisation: sugars, gelatin

100°C – 20 min - 3 successive days
MOIST HEAT

STEAMER
Steamer


Temp >100°C : (Steam under pressure)
Autoclaves
MOIST HEAT
A simple autoclave; 1. release valve; 2. safety valve; 3. pressure gauge; 4.
tightening screws; 5. cover; 6. body; 7. bin containing material; 8. heating
element; 9. stand

STERILISATION CONTROL
Physical

Temperature and pressure monitoring
gauges, thermocouples
Chemical

Bowie–Dick tapes

Biological

Bacillus stearothermophilus 106
spores

FILTRATION
- Heat labile fluids - sera, antibiotics, enzymes,
toxins
- Separation of virus from bacteria
Types of filters:
Candle filters
Berkfeld & Mandler: Made of kieselghur, graded
porosity, sterilised by steaming or autoclave
Chamberland or Doulton: Made of unglazed
ceramic

FILTERS

Asbestos filters:
Seitz filter: - pad of asbestos - inserted into
metal holder - discarded after use
Asbestos filter

FILTERS

Sintered glass filters:
Used for air filtration, made of finely
ground
glass
Glass filter

Membrane filters:
Cellulose nitrate
- Also called gradacol MEM
- To separate viruses, to know their size
Cellulose acetate or millipore filters or oxoid MEM
filters
HEPA: High efficacy particulate air filters
Membrane filter
FILTERS

RADIATION
Non-ionising radiation - Infrared and ultraviolet
rays - low energy type ,low penetrating power
- Control of closed environment with UV lamp
- Bacteriological laboratory, inoculation hoods,
laminar flow

RADIATION
Ionising radiation - Gamma rays, X rays and
cosmic rays lethal to DNA, have high
penetrative power
No appreciable increase in temperature –
‘cold sterilisation’
Use: Sterilising pharmaceuticals, medical, dental
equipment, sterilising plastics, syringes, swabs,
catheters, oil grease

CHEMICAL METHODS

Alcohols

Protein denaturation and lipid dissolution

Bactericidal, fungicidal

Not effective on spores and viruses

Commonly used - Ethyl alcohol, isopropyl
alcohol

Concentration 60-90% in water
CHEMICAL METHODS

Aldehydes
Active against amino group in protein molecule
Formaldehyde
Used for sterilising instruments, heat-sensitive
catheters, fumigation of wards, sick rooms and
laboratories
Glutaraldehyde

Disinfection of medical equipment like cystoscopes
and bronchoscope

Effective against tubercle bacilli, fungi and viruses
CHEMICAL METHODS

DYES
Aniline dyes

Brilliant green, malachite green and crystal
violet

Non-toxic, non-irritant

Active against Gram-positive organisms

Used as selective agents in culture media
Acridine dyes

Proflavine, acriflavine and euflavine

Impair DNA, destroy the reproductive
capacity of the cell

Phenols

Lister - antiseptic surgery

Distillation of tar between 170°C and 270°C

Damage to cell membrane, release cell
contents and cell lysis

Cresols, chlorhexidine, hexachloraphane

Disinfection of floors, excreta, preoperative
disinfection of skin
CHEMICAL METHODS

Halogens
Iodine – Skin disinfectant

Bactericidal, sporicidal

Iodophores more active
Chlorine – Used as hypochlorite

Bactericidal

Disinfect water supplies, swimming pools and
used in diary industries
CHEMICAL METHODS

GASES
Ethylene oxide
- Kills microorganisms by altering their DNA by
alkylation of amino carboxyl, hydroxyl and
sulphydryl groups in protein molecules
- Used in sterilising packaged and heat-sensitive
devices
- Respirators, heart–lung machines, dental
equipment, sutures, books and clothing

GASES
Formaldehyde

Fumigation of theatres and rooms
 150 g of KMnO4 to 280 ml formalin for every
1000 cu ft.

Doors sealed, opened after 48 hrs
Betapropiolactone (BPL)

Condensation product of ketane and
formaldehyde

Hydrogen peroxide fogging

Short cycle time, non-toxic

GAS PLASMA STERILISATION

Plasma is known as the fourth state of
matter.Plasma consists of ions, electrons and
neutral particles.

Radio frequency energy is applied to create an
electromagnetic field- into this Hydrogen
peroxide vapours are introduced which
generates a state of plasma containing free
radicles of hydrogen and oxygen

Used for arthroscopes, urethroscopes

SURFACE ACTIVE AGENTS

Act by altering energy relationship at
interfaces - reduction in surface tension
Classification

Anionic, cationic, amphoteric, non-ionic

Antibacterial, fungicidal, virucidal

Cetavlon, cetrimide


Copper, silver, mercury

Combine with sulphydryl groups of cell
enzymes, denaturation of enzymes

Highly toxic

Thiomersal, mercurochrome less toxic, used
as mild antiseptics

Copper salts - fungicide
SALTS OF HEAVY METALS

Spaulding Classification

Eagle H Spaulding believed that the method
used to disinfect an object will depend on the
object’s intended use
DISINFECTION

WHICH PROCEDURE TO USE?
Category Items in each category Procedure
Critical Items that: (1) enter the tissue; (2) Enter
vascular system; (3) through which
blood flows
High level
disinfection
Semi-critical Items that: (1) touch mucous
membranes; (2) touch non-intact skin
(e.g. endoscopes, respiratory therapy
equipment, thermometer)
Intermediate
level disinfection
Non-critical Items such as bedpans, blood pressure
cuffs, and bedside tables
Low level
disinfection

Sterilisation and disinfection

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