1. Disinfection & Sterilization
Dr : Dina Ramadan
Microbiologist In Central Health Laboratory
Ministry of Health
Quality Manager
Training Workshop on “Laboratory Risk Management”
2-4 Oct, 2012, • Cairo, Egypt

2. Definitions
Disinfection:
It is a procedure intended to reduce microorganisms as far as
possible (but not bacterial spores) by physical and
chemical means
Sterilization:
the complete removal or destruction of all forms of
microbial life including bacterial spores
Remember :
No absolute assurance that there is 0 microorganism

3. Other Definitions
Disinfection
The use of a physical or chemical procedure to eliminate
pathogenic microorganisms on inanimate objects
Sterilization
The use of a physical or chemical procedure to destroy
all microbial life, including large numbers of
highly resistant bacterial spores.

4. Chemical Disinfectant

5. Alcohols
• There are two water-soluble alcohol can be used
in lab: ethyl alcohol and isopropyl alcohol.
• Concentration required : 60-90% in water
• Mode of its action : it denaturing bacterial proteins
• its Flammable, Can be removed from disinfected
articles by flaming.

6. Alcohols effect on bacteria
• they are bactericidal against for the vegetative
forms of bacteria (Gram + and Gram -);
• also they are tuberculocidal, fungicidal, and
virucidal against enveloped viruses (HIV, influenza
,herpes viruses).
• not effective against bacterial spores and have
limited effectiveness against nonenveloped viruses
( adenovirus, rotavirus)

7. Alcohols
• Higher concentrations are
less effective as the action
of denaturing proteins is
inhibited without the
presence of water

8. Hypochlorite's
• it has broad spectrum antimicrobial
effect
• inexpensive and fast acting,
• It is recommended for disinfection of
counter tops and work surfaces,

9. Chlorine
• It is very effective against vegetative bacteria and
viruses like HBV and HIV viruses, therefore its
use is recommended at 1:10 dilution for
disinfection of blood spills
• not much useful against spores

10. Phenol
• It effective against bacteria
(especially gram +ve bacteria)
and enveloped viruses.
• They are not effective against non
enveloped viruses and spores.
• This compounds is used for decontamination of
the hospital environment, including laboratory
surfaces.

11. No Disinfectant is substitute for the
following Procedures
• Hand washing (hand hygiene);
• use of personal protective equipment
(PPE )in the lab
• Environmental cleaning
• Appropriate handling of waste and
• Taking care of yourself (e.g. immunization)

12. Yet no substitute for washing hands
Do not forget to Wash Your Hands
Immediately on arrival at work
After handling specimens
After removing gloves
After using the toilet
Before leaving work

13. Sterilization
1. Heat sterilization
2. Chemical sterilization
3. Radiation sterilization

14. Heat Sterilization
It is the simplest, most effective and inexpensive
method.
Types of heat sterilization :
a) Steam sterilization (Autoclaving)
b) Dry heat sterilization

15. Mechanism of Action
• DRY HEAT • MOIST HEAT
• protein denaturation 1. Protein denaturation &
1. Oxidative damage coagulation
2. Toxic effects of 2. Latent heat liberated
increased levels of when steam condenses on
electrolytes cooler surface
3. Hydrolysis & breakdown
of bacterial proteins

16. Steam Sterilization (MOIST HEAT )
Advantages:
– good penetration
– maintains integrity of liquids (e.g. Lubricants) due
to the 100% humidity within the chamber.
Disadvantages:
– Non stainless steel metal items corrode
– may damage plastic and rubber items

17. Dry-Heat Sterilization
• Heating at atmospheric pressure and often use a fan to
obtain uniform temperature by circulation.
• Heat at 180º for half hour , 170º for 1 hr., or 160º C for 2
hrs.
Temperature (°C) Time (minutes)
120 480
140 180
150 150
160 120
170 60
180 30

18. Dry-Heat Sterilization
• Advantages:
• It is effective and safe for metal instruments because
the process does not dull instrument edges or
rust/corrode the instruments.
• Disadvantages:
– Less reliable than autoclaving
– Many materials do not tolerate
dry heat (as media)

19. Chemical Sterilization
• The chemical compounds used can be:
a) Gas Sterilization
b) Liquid Sterilization
• Generally, chemical sterilization procedures
have the disadvantages of presenting health hazards
to users (e.g. poisonous, flammable, )

20. Gas Sterilization
• The gas used in this procedure is ethylene oxide.
• Keep objects in constant atmospheric humidity.
• Heat to temperatures between 30º and 60º C,for a
period of 10 hrs.
• Residual ethylene oxide must be ventilated
• It is used for sterilizing endoscopes and ansthetic
apparatus.

21. Liquid Sterilization
• Can be performed with buffered glutaric aldehyde.
• Procedure:
– Immerse object in liquid for several hours.
– Rinse with sterile water after end of procedure.
– It used in hospitals for sterilization of surgical
instruments, rubber or plastic equipment
which cannot be heat sterilized

22. Radiation Sterilization
• Provides effective way of sterilization when
using non ionizing radiation in high doses
(Gamma radiation ).
• it is clean process
• dry process
• the object full exposure from all directions

23. Non ionizing radiations
• UV RAYS (ultra violet)
are used to sterilize internal Surfaces of safety
cabinets, entry ways, Operation theaters etc.
• IR RAYS ( infra red)
are used for rapid mass sterilization of pre packed
items such as syringes, catheters etc.

24. Sterilizing Filter
• Aqueous liquids sterilized by forced passage through filter of
porosity small enough to retain any microorganism.
1) Membrane filters:
• Manufactured from variety of polymeric material such as
cellulose diacetate, polycarbonate and polyester, as
disc.
• Membrane made in 2 ways
I. Labyrinthine pore membranes: Bacteria & yeast
II. Capillary pore membranes: For viruses
Filters may be supplied with plastic holders pre sterilized for single
use, or mounted in re-usable holders and fitted to filtration
vessels.

25. Sterilizing Filter
2)Syringe filters:
• Membrane 13-25mm diameter.
• Fitted in syringe like holders of stainless steel or
polycarbonate.
• Used for sterilization of small volumes of fluid.
3)Vacuum and in- line filters:
• Membranes of 25-45 mm diameter are used either
with in line filter holders of Teflon or stainless
steel and aluminum.
• Used for sterilization of large volumes of air and
liquid.

27. In summary
• Sterilization and disinfection are costly and time
consuming process
• However, it is an essential in all health care
facilities to avoid infection.
• It depends the material and users of instrument.
• Staff should keep in mind that contaminated
instrument present risk to the sample as well as
the user himself.

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