Disinfection and sterilization

1. Safety and biosecurity
Laboratory Lecture 6:- Disinfection and sterilization
Dr. Raghda Saad Mohammed

2. Definitions
Many different terms are used for disinfection and sterilization. The
following are among the more common in biosafety:
• Antimicrobial – An agent that kills microorganisms or suppresses
their growth and multiplication.
• Antiseptic – A substance that inhibits the growth and development of
microorganisms without necessarily killing them. Antiseptics are
usually applied to body surfaces.
• Biocide – A general term for any agent that kills organisms.
• Chemical germicide – A chemical or a mixture of chemicals used to
kill microorganisms

3. Definitions
• Decontamination – Any process for removing and/or killing
microorganisms. The same term is also used for removing or
neutralizing hazardous chemicals and radioactive materials.
• Disinfection – A physical or chemical means of killing
microorganisms, but not necessarily spores.
• Microbicide – A chemical or mixture of chemicals that kills
microorganisms. The term is often used in place of “biocide”,
“chemical germicide” or “antimicrobial”

4. Definitions
• Sporocide – A chemical or mixture of chemicals used to kill
microorganisms and spores.
• Sterilization – A process that kills and/or removes all classes
of microorganisms and spores.

5. Various agents used is sterilization are:
A. physical method
B. chemical method
A. physical method
1-Sun light 2- drying 3- heat 4- filtration 5-radiation
1-Sun light : it bactericidal activity. the action is due to ultraviolet ray.
2-Drying : drying in air has effect on many bacteria.
3-heat : the factors influencing sterilization by heat are :
a-Nature of heat
b-Temperature and time
c-Number of organisms
d-Whether organism has spore capacity

6. Type of heat
1-Dry heat
A-Red heat: it is used to sterilize metallic objects by holding them in a flam till they
are red hot ex Wire loop , needles scalpels forceps, etc.
B-Flaming: the article is passed over flam without allowing it to become red hot
e.g. culture tubes, glass, slides
C- Hot air oven: requires temp- of 160 c for one hour - we can sterilize all glass,
syringes , petri-dishes , test tubes flask , etc
2- Moist heat: the lethal effect is by denaturation and coagulation of protein
A- Temp. below 1000C
Pasteurization of milk :temp. employed is either : 63C for 30 mints holder method
or: 72 C for 15-20 second flash method
Mycobacterium , Salmonella , Brucella are killed

7. B- Temp. at 100C.
1- Boiling : most of vegetation from bacteria , fungi and are killed 50-70 C
in short time for needles and instruments boiling in water for 10-30 min , is
sufficient to Sterilization.
2- Steam under pressure : autoclave is used for bacteriological and
surgical work because of spores kills all microorganisms including (HIV &
hepatitis virus).
Filtration ;- Is the method of sterilization, used filter paper useful for
antibiotic solutions , sera , etc.
Radiations
Ultraviolet radiations : it is chief bactericidal factor present in sun light , it
cause following changes in cell
1. denaturation of protein
2. damage to DNA
3. inhibition of DNA replication

8. B-Chemical methods:
1- Acid and alkaline: growth bacteria inhibition Mycobacterium is more
resistant to acid than alkaline
2-Halogens: iodine is used chiefly for skin. combines with water to from
hydrochloric acid which is Bactericidal.
3 -Formaldehyde: useful in sterilization . It is lethal to bacteria and their
spores ,viruses and fungi .
4- Soap and detergents: they are Bactericidal and bacteriostatic for gram
positive bacteria and some acid fast organisms.
5-Aerosol and gaseous disinfectants : chlorine and formalin vapor have
been used as gaseous disinfectant . Propylene, glycol is powerful
disinfectant

9. Thanks for
your
attention
9/17/2022
9