sterilisation


Early civilizations practiced salting, smoking, pickling,
drying, and exposure of food and clothing to sunlight to
control microbial growth.

Use of spices in cooking was to mask taste of spoiled
food. Some spices prevented spoilage.

Low water content or low pH prevents microorganisms
multiplying

In mid 1800s Semmelweiss and Lister developed
aseptic techniques to prevent contamination of
surgical wounds.
• Nosocomial infections caused death in 10% of
surgeries.
• Up to 25% mothers delivering in hospitals died due to
infection

Practices, emphasizes
the importance of
washing hands with
chlorinated water in
Obstetrics to reduce
maternal mortality


1867 –Dr.Joseph Lister first
identifies airborne bacteria
and used Carbolic acid
spray in surgical areas
1880 – Johnson and
Johnson introduce antiseptic
surgical dressings.




Lister era 1868 changed the
concept of safe surgical
procedures.
Carbolic Acid in
decontamination caused
Reduction of Hospital
associated infections
Mortality reduced
Morbidity reduced.

Laboratory work with pure cultures requires the use of
apparatus and culture media that is sterile

Prevention of infection in patients requires the use of
equipment, instruments, dressings and parenteral drugs
that are free from living micro-organisms

Sterilization is the process of killing all the
microorganisms in all its forms inclusive of bacterial
endospores in a preparation/article such as lab media,
surgical instruments and equipment.

A sterile environment is free of life of every kind.
Disinfection: Reducing the number of pathogenic
microorganisms to the point where they no longer
cause diseases.
 Usually involves the removal of vegetative or nonendospore forming pathogens.
May use physical or chemical methods.
Fumigation:
Process of disinfection by fumes of vaporized
germicide
Sepsis: Comes from Greek for decay or putrid.
Indicates bacterial contamination.
Asepsis: Absence of significant contamination.
Aseptic techniques are used to

prevent contamination during surgery.

prevent bacterial contamination in food industry
ANTISEPSIS: Is the prevention of infection by inhibiting
the growth of bacteria.
ANTISEPTICS: Chemical disinfectants which can safely be
applied to skin or mucus membranes to prevent infection.
CONTAMINATION: Soiling of an article, food or water
with microbes by contact is known as soiling.
DECONTAMINATION: Soil-removing process which
removes many of microbes
Disinfectant:
Applied to inanimate objects.
Antiseptic:
Applied to living tissue (antisepsis).
Degerming:
Mechanical removal of most microbes
in a limited area.
Sanitization:
Use of chemical agent to reduce the
microbes to minimize chances of disease
transmission. Eg: Hot water & soap
Bacteriostatic Agent: An agent that inhibits the growth of
bacteria, but does not necessarily kill them
Germicide: An agent that kills certain microorganisms.
Bactericide:
An agent that kills bacteria. Most do not kill
endospores.
Viricide:
An agent that inactivates viruses.
Fungicide: An
agent that kills fungi.
Sporicide: An
agent that kills bacterial endospores & fungal
spores.
CLASSIFICATION:
A. PHYSICAL AGENTS:
1. SUNLIGHT
2. DRYING
3. HEAT
A. Dry Heat (a) Red heat.
(b) Flaming.
(c) Incineration.
(d) Hot Air Oven.
B. Moist Heat
(a)
(b)
(c)
(d)
:
Temperature below 1000C.
Pasteurization.
Inspissation.
Temperature at 1000 C:
Ex: Boiling
Steam under normal pressure.
Ex: Tyndallization
Steam under pressure.
Ex: Autoclave
2. FILTRATION.
(A) Candle filters.
(B)
Asbestos pads (Seitz filter)
(C)
Sintered glass filter.
(D)
Collodion or membrane filters.
(E)
HEPA filters.
3.
RADIATION.
4.
ULTRASONIC AND SONIC VIBRATIONS.
B)CHEMICAL AGENTS:
1) Alcohols
2) Aldehydes
3) Gases
4) Halogens.
5) Phenols
6) Dyes
7) Surface active agents.
8) Metallic salts.

D.value (Decimal reduction value):
Dose required to inactivate 90 % of the initial
microbial population.
This varies with different species.
Escherichia coli : Few minutes.
Salmonella spp :One hour.
At 700 C Staphylococcus aureus : One minute.
S. epidermidis : Three minute.
Damage of DNA
Protein denaturation
Disruption of cell membrane or cell wall
Chemical antagonism
Removal of free sulfa hydryl group
Factors influencing the death of microbes.
1. Number of Microbes: The more microbes present,
the more time it takes to eliminate population.
2. Type of Microbes: Endospores are very difficult to
destroy. Vegetative pathogens vary widely in
susceptibility to different methods of microbial control.
3. Environmental influences: Presence of organic
material (blood, feces, saliva) tends to inhibit
antimicrobials, pH etc.
4. Time of Exposure: Chemical antimicrobials and
radiation treatments are more effective at longer
times. In heat treatments, longer exposure
compensates for lower temperatures.

Heat:
Kills microorganisms by denaturing their
enzymes and other proteins.
Heat resistance varies widely among microbes.

Thermal Death Point (TDP):
Lowest temperature at which all of the microbes in
a liquid suspension will be killed in ten minutes.
 Thermal Death Time (TDT): Minimal length of
time in which all bacteria will be killed at a given
temperature.
 Decimal Reduction Time (DRT): Time in minutes
at which 90% of bacteria at a given temperature will
be killed.

Spontaneous sterilisation in natural environment

Due to UV rays and heat rays

Moisture is essential for growth of bacteria

Deleterious effect on many bacteria

Unreliable method

No effect on spores

Flaming

Red heat

Incineration

Hot air oven

Dry Heat: Kills by protein and enzyme
denaturation, oxidation & toxic effect of elevated
levels of electrolytes.

Flaming glass slides, mouth of the culture bottles

Red heat inoculating loops and needles. Heat metal
until it has a red glow

Incineration: Effective way to sterilize disposable
items and biological waste.
Red Heat:
1.
•
Instant method of sterilization.
•
The articles to be sterilized are held in Bunsen
flame till they become red hot.
•
Ex : Inoculating wires, Tips of forceps, Scalpels,
Searing spatulas, Needles.
2. Flaming :

This method is of uncertain efficacy.

The articles has be passed a few times through the Bunsen
flame but not allowed to get red hot.

Ex: Glass slides, Cover slips, Mouths of culture tubes
INCINERATION :

Excellent method for rapid destruction of Soiled
dressings, Animal carcasses, Pathological specimens.

Effective way to sterilize disposable items

But Polystyrene materials emit clouds of dense black
smoke.

Reduced to ashes by burning.

Temperature at which it works is 7000 C - 9000 C.
Incineration is a process where by combustible materials are
converted into non combustible residue or ash ;achieving reduction
in weight or volume .
consists of two chambers –primary& secondary .
◦ Primary –temp of 750-8500c
◦ Secondary – temp of 1000-1100 0c
Chimney of incinerator –30 mts high
combustion efficiency –99% .

Most widely used sterilizer by dry heat.

Electrically operated instrument.

Hot air is a bad conductor of heat and its penetrating
power is low.

Fitted with fans for adequate air circulation in the
chamber.

Holding time & temperature : 1600 C for 2 hrs or
1800 C for 30 min.
Uses:
1.
Glassware: Syringes, Petri dishes, test tubes, flasks,
pipettes, etc.
2.
Surgical instruments (forceps, scalpels, scissors).
3.
Oily fluids ( Liquid paraffin)
4.
Chemical & dusting powders, sulphonamides
5.
Swabs
6.
Silicon rubber only (not other rubber material)
7.
Fats, Grease
Precautions:
1. Articles should be absolutely dry & wrapped in
paper.
2. Not suitable for rubbers, fabrics, inflammable or
volatile substances.
3. It should not be overloaded.
4. The oven should be allowed to cool for 2 hrs before
opening the doors to prevent cracking of glassware.
1. Decontaminate, clean, and dry the items
2. Wrap items using foil, double-layered cotton, craft
paper or muslin fabric;
3.
Put unwrapped items on a tray or shelf;
4.
Place instruments and other items in a metal, lidded
container
5. Place in the oven, and heat to the designated
temperature.
170 degrees C (340 degrees F) - 1 hour
160 degrees C (320 degrees F) - 2 hours
150 degrees C (300 degrees F) - 2.5 hours
140 degrees C (285 degrees F) - 3 hours
Cutting instruments sterilized for 2 hours at 150oC
For oils, glycerol, dusting powder – 1hour at 150oC
◦ Dry heat can dull sharp instruments and needles, these
items should not be sterilized at temperatures higher
than 160 degrees C.
◦ Leave items in the oven to cool before removing.
◦ When they are cool, remove items using sterile pickups
and use or store immediately.
Sterilization control:
1. Spores of non-toxigenic strains of Cl.tetani.
Paper strips impregnated with 106 spores are placed in
envelops & inserted into suitable packs. Then inoculate
into thioglycollate or cooked meat broth & incubate under
strict anaerobic conditions for 5 days at 37oC .
2. Browne's tube (green spot): This is convenient for
routine use. After 60 minutes at 160oC or 115 minutes at
150oC.
3. Thermocouples may also be used.

Mechanism – Dessicates oxidation of essential cell
constituents

Advantage- Ease of employment, Penetrates oilbased materials and closed container

Disadvantage-Poor power of penetration, slow
sterilizer, high temperature.