microbiology

1. Sterilization
&
Disinfection
By
Eman A.Abd Alrahman
Ass. Lecturer of Microbiology
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2. Sterilization is the killing of all living forms of
microbes including their spores.
Disinfection is the destruction of most but not
necessarily all pathogenic microbes or their spores
Decontamination is a term applied to any
procedure that reduces pathogenic
microorganisms to a level where items are safe for
handling, for use or disposal. It can be done by
cleaning, disinfection or sterilization. 2

3. Cleaning is a process that removes foreign
material (e.g. dirt, organic material, and some
microorganisms). Cleaning must precede
disinfection and sterilization. It is usually done
with soap and water, detergents or enzymatic
products.
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4. Method of Sterilization
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5. A- Sterilization by Heat
1-Dry heat:- kills by destructive oxidation of
essential cell constituents. It is less efficient than
moist heat. However, it is less expensive and is not
corrosive
a) Red heat : bacteriological loop & forceps
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6. b) Flaming : used for the mouth of tubes and
glass slides.
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7. c) Incineration: used for contaminated
materials by burning in a special incinerator.
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8. d) Infra red radiation : used for surgical
instrument, temp: 180 °C.
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9. e) Hot air oven
•Composition :isolated double
walled chamber electrically
heated, provided with
thermotstate and a fan to
ensure rapid and controlled
heating .
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10. •Tempreture:160 °C
•Holding time :1.1/2 hour (after temp reach 160
°C
•Used for: sterilization of glass ware, ointments,
powders, oils and metallic instruments.
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11. Moist heat
Under 100 oC
• Pasteurization
•Inspissation
At 100 oC
• Boiling
• Tyndallisation.
Over 100 oC
•Autoclaving
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12. Moist heat
kills bacteria by protein denaturation.
a)Temperature below 100 °C
1- Pasteurization: as pasteurization of milk
by heating at 63oC for 30 min. or at 72 °C
foe 20 sec. and immediately cool below 10 °C
• This kills non spore forming milk borne
pathogens e.g. M.tuberculosis, Br.abortus,
Salmonella and Coxiella burnetti. 12

13. 2-Inspissation: Heating at 85 ̊C for 30 min,
for 3 successive days.
•Used for sterilization of media containing
egg.
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14. b) Temperature of 100 oC
1-Boiling:
Used for disinfection of
surgical and medical equipment
when sterility is not required.
 Boiling occurs at 100 °C for
20 min. and enhanced by
adding 2% Na bicarbonate.
 Kills all vegetative bacteria
and HBV but not spores. 14

15. 2-Sterilization by tyndalization (heating at
100oC for 30 min, for 3 successive days)
• At first day vegetative bacteria are killed and
spores germinate to vegetative which will be
killed in 2nd and 3rd days.
• Used for sterilization of media containing
sugars or gelatin.
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16. c)Temperature above 100°C
(Steam sterilization or autoclaving):
Principle: When heating water in a closed vessel,
boiling point rises above 100°C.
Conditions of sterilization: Heating at 121°C under
2 atmospheric pressure for 20-30 min. or at 134°C
under 3 atmospheric pressure for 3-6 min. (flash
autoclave)
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17. Autoclaving is the most efficient method of
sterilization.
Why?
 High temp.
 High penetration power of steam under
pressure.
Condensed steam liberates large amount of
latent heat.
 Not toxic, inexpensive and rapid. 17

18. Monitoring of autoclaves:
1- Mechanical methods: monitoring time, temperature
and pressure of sterilization cycle.
2- Chemical methods:
Bowie Dick tape is applied to articles being autoclaved. If
the process has been satisfactory, dark brown stripes will
appear across the tape. Pale brown stripes are suggestive
of poor heat penetration, and an unsatisfactory
sterilization process.
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19. 3-Biological indicator:
Geobacillus stearothermophilus spores strips may be
placed inside the autoclave at the start of its cycle.
After running, the autoclave the strip is recovered
and cultured. Absence of growth after a suitable
period indicates a successful run.
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20. Types of Autoclave
Automated autoclave Simple autoclave
Flash autoclave 20

21. Sterilization by radiation
• Ultraviolet rays
• Poor penetration power
• Source: mercury vapor lamp
• Sterilization of air and water
• Can cause eye damage
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22. • Ionizing radiation
• High penetration power
• Source: radioactive isotope as cobalt 60, β rays
and gamma rays
• Sterilization of materials not stand heat as plastic
syringes, gloves, catheters.
• Monitoring: By spore indicator (B. pumilus)
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23. Filtration
• It is a mechanical method for exclusion of
organisms from biological fluids which are
destroyed by heat e.g. serum, plasma,
hormones, vitamins and fluid culture media.
Also sterilization of air in operation rooms,
drug filling cubicles.
• It depends on use of filters with pore size
smaller than that of bacteria so retain them.
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24. 1)Vacuum filter(Seitz):
Used for sterilization of
large volumes of fluids.
suction is applied to side
tube to force fluid to pass
through the filter.
Types of filters:
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25. 3-Millipore filter:
Suitable for sterilization of
small amounts of fluids.
4- Air filters:
HEPA (high efficiency particle arrester)
filter.
Used to decontaminate air input to
operation rooms and air withdrawn
from areas of dangerous pathogens.
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26. Gaseous sterilization
a)Ethylene oxide (EO)
• Ethylene oxide bactericidal & sporicidal
• capable of killing spores rapidly by interfering with
the normal metabolism of protein and reproductive
processes, resulting in death of cells.
• Sterilization of heat sensitive devices e.g. plastic
and rubber articles, heart lung machines.
Chemical sterilization
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27. Sterilized articles exposed to gas at 55 °C for 3 –
6 h then aerated for 8-12 h.
• Bacillus atrophaeus spores are used for
monitoring EO
Disadvanteges
Toxic , explosive and carcinogenic requiring safety
precautions .
 Colorless gas ,very toxic and flammable .
 Requires special equipment.
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28. Materials must be well aerated after sterilization .
 takes longer time than steam sterilization.
 Long-term exposure to EO is potential
occupational carcinogen causing leukemia.
Over exposure cause nasal and throat irritation
Prolonged exposure may result in nausea, vomiting
dizziness, difficulty breathing and peripheral paralysis.
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29. Sterilization by ethylene oxide (EO)
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30. Gas plasma
• Plasma: any gas consists of electrons, ions or neutral
particles
• Hydrogen peroxide alone or with peracetic acid
are injected into sterilization chamber under
pressure to evaporate and surround items to be
sterilized then radiofrequency energy is applied
which excites Hydrogen peroxide and produce
plasma containing free radicals which are lethal to
bacteria. 30

31. Uses: Sterilization of surgical instruments with long
narrow lumen as laparoscopes
Advantages of Gas plasma
1. The process is dry and nontoxic; items do not need
to be dried or aerated.
2. Low temperature allows safe sterilization of some
heat sensitive items, including endoscopes and fiber
optics.
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32. 4. Plasma has significantly less effect on metal
than steam sterilization corrosion does not
occur.
5. The sterilizer is simple in design, and
connects to standard
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33. Gas Plasma Sterilizer
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34. Others
Used forExamples
Clinical thermometer& skin antisepticEthyl alcohol 70%
Skin antisepticIodine (tinc.iodine or betadine)
Water and swimming poolcholrine
Wound antisepticHydrogen peroxide
endoscopeGlutraldehyde
Wound infectionSalts of heavy metals
mercucrome
Culture decontaminationPhenol
Room disinfectionFormaldehyde
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