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Sterilization: complete removal, destruction,
inactivation of all forms of microbial life
viruses,
Fungi,
bacteria,
Spores.
• Disinfection: elimination of most pathogenic
organisms excluding sporicidal activity. There
are 3 levels;
• HLD, all vegetating bacteria, MTB, fungi, all
viruses
• ILD, all vegetating bacteria, MTB, majority
of fungi, majority of viruses
• LLD, vegetating bacteria except MTB,
some fungi, some viruses
•Antiseptics: chemical disinfectants applied to
skin, mm but not systemic
•Cleaning: removal of dust, dirt, organics, FM.
•Decontamination: general term applied to any
procedure by which microorganisms are
reduced to a level where items are safe to
handle
Patient’s care items are divided into 3
categories:
Critical items
Semi-critical items
Non-critical items
Depending on the risk of infection due to their utilization
Critical
Semi critical
Items enter -sterile
tissues-cavitiesvascular system
Items come in
contact with
intact mm &
non intact skin
e.g. needles,
implants, catheters,
surgical instruments
e.g. endoscopes,
endotracheal tube,
thermometer
Sterilization: EO,
autoclave,
plasma, sterilant
High level disinfectant,
glutaraldehyde, chlorine
active, hydrogen
peroxide
Noncritical
Items come in
contact with intact
skin
e.g.
sphygmomanometers,
bed linens, floors
Intermediate and low
level disinfectants,
alcohols, phenols
Decreasing order of resistance of microorganisms
to disinfection and sterilization
Resistant
•
•
•
•
•
•
•
Susceptible
•
•
Prions
Bacterial spores
Mycobacteria
Small non-enveloped
viruses
Gram-negative bacteria
Fungi
Large non-enveloped
viruses
Gram-positive bacteria
Lipid enveloped viruses
Decontamination Steps
I. Heat
1- Moist heat or steam sterilization
2- Dry heat sterilization
II. Low temperature (cold):
1. chemical
a. ethylene oxide
b. liquid steriliants: GLD, PAA, H2O2
2- plasma sterilizer
III. Other sterilizers:
1- ionizing radiation
2- filtration
3- microwaves; in pharmaceutical industries
• Heat is the most practical, efficient, and
inexpensive method of sterilization and
disinfection of objects that can withstand high
temperatures.
• There are two forms:
– Moist heat is much more efficient than dry heat because:
• it kills microorganisms by coagulating and denaturing
their enzymes and structural proteins
• it is quicker in heating up the article to be sterilized.
– Dry heat is believed to kill microorganisms by causing
destructive oxidation of essential cell constituents.
Autoclave = saturated water steam under high pressure.
heating water under controlled conditions in a closed vessel in order
that boiling point of water rises above 100°C.
Saturated steam carries the same temperature of boiling water.
It is essential to make steam saturated and free of any residual air because
air acts as an insulator, reduces temperature and hinders penetration.
Sterilization temperature and exposure time :
at 121°C for 20-30 minutes at double atmospheric pressure (2 bar)
or at 134°C for 3-6 minutes (at 3 bar).
• Steam sterilization is
the most common and
preferred method for
sterilizing those items
that can withstand high
temperature and
moisture, e.g. culture
media, surgical
instruments and
dressings.
Autoclave:
Advantages:
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Non-toxic
liberation of latent heat due to condensation of steam
Inexpensive
Rapidly microbicidal
Least affected by organic/inorganic soils
Rapid cycle time
Penetrates medical packing, device lumens
Disadvantages:
1- Deleterious for heat labile instruments
2- Potential for burns not for powders and oils
Sterilization monitored routinely by
combination of mechanical,
chemical, and biological parameters
• Physical - cycle time, temperature,
pressure
• Chemical - heat or chemical sensitive
inks that change color when
germicidal-related parameters
present
• Biological - Bacillus spores that
directly measure sterilization
(Geobacillus stearothermophilus)
Chemical Indicators
I.
Incineration:
II.
Red heat:
•
•
For dead animal bodies
Infectious hospital waste
for wires, loops, tips of forceps
they are flamed till reach
redness
I.
Hot air oven:
Dry hot air used either
170c for 60 min
or 160c for 120 min
Micro-incinerator
• Hot air oven
- They are electrical devices used in
sterilization.
-There is a digitally controlled
thermostat controlling the
temperature.
- Their double walled insulation keeps
the heat in .
- There is also an air filled space in
between to aid insulation.
- An air circulating fan helps in uniform
distribution of the heat.
Advantage of dry heat
1. Hot air penetrates certain substances that cannot be steam
sterilized (oil, powder).
2. Dry heat can be used in laboratories to sterilize glassware
3. Dry heat is a protective method of sterilizing no erosion or
corrosion.
4. Instruments that cannot be disassembled may be sterilized in hot
air.
5. Low cost
Disadvantages of dry heat
1. A long exposure period is required because hot air penetrates
slowly possibly unevenly.
2. Time and temperature vary for different substances.
3. Over exposure may ruin some substances.
4. It is destructive to fabrics and rubber goods
Monitored by B.subtilis spores
• Ethylene oxide gas is commonly used to sterilize objects sensitive to
temperatures greater than 60 °C such as plastics, optics and electrics.
• Ethylene oxide penetrates well, moving through paper, cloth, and some
plastic films and is highly effective.
• Ethylene oxide sterilizers are used to process sensitive instruments
which cannot be adequately sterilized by other methods
• Advantages
–
–
–
–
Very effective at killing microorganisms
Penetrates medical packaging and many plastics
Compatible with most medical materials not withstanding heat
Cycle easy to control and monitor
• Disadvantages
– Some states require ETO emission reduction of 90-99.9%
– (inert gas that eliminates explosion hazard) banned after 1995
as it is inflammable
– Potential hazard to patients and staff (very toxic and
carcinogenic in animal models)
– Lengthy cycle (3-6 hrs)/aeration time (18-24hrs)
Monitored by B. subtilis spores
Plasma describes any gas that consists of
electrons, ions, or neutral particles.
Plasma sterilizers with the use of liquid peracetic
acid, or hydrogen peroxide, or a mixture of both
are commercially available.
The energy used is either microwave frequency or
radio-frequency.
1- Gamma rays (Co-60).
2-High energy electrons (electron accelerator).
This process does not result in rise in temp; but the
time required for sterilization is long (48hrs).
High penetration power so used in prepacked items, as gloves,
syringes, plastic IV lines,…
Monitored by B.pumilus spores
• Sterilization of fluids which would not
withstand heat such as antibiotic
solutions, blood products, hormones,
vitamins….etc.
• Fluids can be rendered free of bacteria by
passage through filters with a pore size of
less than 0.45 µm.
– However, most viruses and certain bacteria as
mycoplasma can pass through filters with a
pore size as small as 0.22 µm.
Filtration: Fluids
• Early filters made from glass and asbestos
– largely replaced by membrane filters made of
cellulose esters or other polymers.
• Membrane filters are preferred because:
– they filter more rapidly.
– they don't affect the filtrate in any way.
– they adsorb very little of the substance being filtered.
–
• The endopigment producing Serratia
marcescens can be used to test the efficiency of
bacterial filters.
• Filters can be used to remove microorganisms
from air supplied to critical areas such as
operating rooms, drug factories and laminar flow
ventilation system.
• A properly installed high efficiency particulate air
(HEPA) filter can achieve 99.997% arrest to
particles ≥ 0.5 µm, and can produce sterile air.
• Spores of the fungus Aspergillus can be used to
test the efficiency of HEPA filters.
Filtration: Air
1- Chemical disinfection
2- Boiling water
3- Pasteurization
4- Ultraviolet irradiation
1- Alcohol 70% (ethyl and isopropyl):
Exposure time: 5 min at least
Uses: 1- disinfection of
a. external surfaces
b. non invasive instruments
2- skin antiseptic, alone or added to iodine or
chlorhexidine
2- Biguanides (chlorhexidine):
1- antiseptic for skin and mm, mouth wash (hexitol)
2- combined with
. Alcohol as hand rub
. Detergent as hand wash
3- Chlorine- active compounds (hypochlorite, house hold
bleach):
1- decontamination of blood splashes and lab. Working
surfaces (100-1000ppm)
2- linen bleaching
3- disinfection of water
4- Iodine based compounds (most effective antiseptics):
include - tincture iodine (iodine in alcohol), staining and
irritant
- iodophores (iodine with neutral carrier), slow
release of free iodine, more penetration, no staining
and not irritant, betadine (30-50ppm)
used as skin antiseptic in surgical scrubbing and
before surgery.
Both halogens exert their bactericidal action by irreversible oxidation of the
essential enzymes by the free radicals
5- Phenol containing preparations (phenol\lysol) ILD:
Used for floors, walls and furniture
Hexaphenol (detol) was used as antiseptic, was proven to
cause neurological damage
6- Quternary ammonium compounds LLD:
detergent either .anionic as soap
or . Cationic as LLD
.
Used for routine cleaning of walls, floors or furniture.
7- Hydrogen peroxide: (oxidizing agent) HLD& sterilants
1- antiseptic for open wounds( kill anaerobes)
2-disinfection of soft contact lenses, some endoscopes
8- Peracetic acid: (oxidizing agent) HLD& sterilants
HLD, strilizant of instruments as endoscopes
9- Glutaraldehyde(cidex) and Formaldehyde HLD& sterilants:
GLD: HLD, sterilizant of instruments as endoscopes,
respiratory and anaesthesia equipments
FLD: gas not used now, found to be carcinogenic, only used in
sterilization of HEPA filters.
Boiling at 100c for 20 min = HLD
Only in emergencies
It is heating at temperature less than 100c
1- Pasteurization of milk:
heating at 63c for 30 min
or at 72c for 20 sec, this is followed by rapid cooling.
this destroys imp pathogenic bacteria as, MTB, salm,
brucella, coxiella
2- Pasteurization of water:
heating at 77c for 30 min.
used for disinfection of items can’t withstand higher temp
it may be coupled with chemical disinfection to achieve higher
level of disinfection or even sterilization
UV is a low energy, non ionizing irradiation
Its present in sun, artificially produced by mercury
lamps
Over exposure may cause eye damage and skin
irritation
Have extremely weak penetration power
Used only for:
Air and surface disinfection in
Operating rooms
Safety cabinet