sterilization

1. STERILIZATION
Prashantsharma

2. DEFINITIONOF STERILIZATION
Sterilization is defined as, “ the process of complete removal/ elimination of all forms of life (biological agents such as bacteria, fungi,
viruses, spores etc.) present in a specified region such as materials, surface area, culture media to be sterilized.

4. Physical methods for
sterilization

5. Definition – Physical methods refer to the heat,
radiations and mechanical processes used for
sterilization.
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6. Heat
Main role – Temperature
Factors influencing
sterilization by heat -:
Nature of heat Temp. with time
No. of organisms
present
Sporing capacity
Type of material from which
organisms to be eradicated

7. Dryheatsterilization
Dryheatreferstothehotairthatiseitherfreefrom
watervapororhasverylittleofitwherethemoisture
playsaminimalroleornoroleintheprocessof
sterilization.

8.  Dry heat kills microbes using following
destructive methods -:
• Oxidative damage
• Protein denaturation
• Toxic effect of elevated level of
electrolyte
How dry heat kills microorganisms for
sterilization ?

9. Methodsfordryheatsterilization-:
Incineration
Flaming (flame sterilization)
Hot air oven

10. Incineration
It is mainly used to sterilize metallic objects by holding them in flame
till they are red hot.

11. Flaming{Flamesterilization}
Here, the article isfirst dippedinethanol andthen itis
passed over the flamewithout allowing itto get red hot.

12. Hot air oven are the electrical
devices which use dry heat to
Sterilize the material.
Developed by - Pasteur
It uses thermostat to control the
temperature.
Hot airoven

13. Hot airoven
The dry / hydrophobic materials can be sterilized by dry heat in hot air oven.
Mechanism of killing microbes –Oxidation of biological materials.
Operated at – temp.160*C for 2 hours or
temp.190*C for 10min

14. Diagram of hot air oven -:

15. What are the disadvantages of using dry heat as a sterilizing
agent?
Relatively slow i.e. take couple of hours for sterilization
Many objects such as plastics cannot withstand high
temperature required for dry heat sterilization.
The sharpness of metal objects decrease at high
temperature.

16. MOIST HEATSTERILIZATION
• It is a procedure in which heated/high pressured steam is used to sterilize an object.
• This sterilization technique does not involve any toxic liquids or fumes.
• It is capable of eliminating bacteria, viruses, fungi & spores.

17. HOWMOISTHEATCAUSESLETHALEFFECTTOMICROBES?
Moistheatkillsmicroorganismsmainlyby-;
Denaturing&coagulatingtheproteins.

18. TYPES OF MOIST HEAT STERILIZATION
Below temp. 100*c At temp. 100*C Above temp.100*C
Pasteurization Inspissation Tyndallization Boiling Autoclave

19. AUTOCLAVE
• Autoclave is a pressure chamber used to carry sterilization.
• Principle – Steam under pressure
• Invented by - Charles Chamberland in the year 1884.
• Operated at – 120+_1*C &and 15lb pressure for 20 minutes.
• Materials sterilized in autoclave- nutrient media, water, forceps, needles etc.

20. BB

21. WHICH IS MORE EFFECTIVE BETWEEN DRY HEAT & MOIST HEAT
STERILIZATION? GIVE REASON.
Moist heat sterilization is more effective than dry heat sterilization.
Reason – Water is better conductor of heat than air &
also it kills the microbes by coagulating ,
denaturing their proteins, enzymes etc. which
leads to the loss of 3-dimensional functional
shape.

22. RADIATIONS
• Radiation is defined as the “ emission of energy as electromagnetic waves or as moving high energy subatomic particles
which cause ionization”.

23. TYPESOF RADIATIONSUSEDFORSTERILIZATION
Ionizing radiations Non-ionizing radiations
Gamma rays X-rays Ultra violet rays Infrared ray

24. LAMINAR AIR FLOW
• A laminar flow cabinet or laminar flow closet is a carefully enclosed bench designed to prevent contamination of biological
samples, or any particle sensitive materials.
• Laminar air flow does sterilization by using “ultraviolet light”.
• Air is drawn through a HEPA filter and blown in a very smooth, laminar flow towards the user.
• Due to the direction of air flow, the sample is protected from the user but the user is not protected from the sample. The cabinet is
usually made of stainless steel with no gaps or joints where spores might collect.

25. STRUCTURAL ANALYSIS OF LAMINAR AIR FLOW

26. HOW ULTRAVIOLET LIGHT KILLS MICROORGANISMS ?
Ultraviolet light kills the microbes by damaging
the genetic material with the formation of
thymine dimers.
The distance , time of exposure and intensity
of UV light are important for its lethal effect.

27. FILTRATION
Filtration helps to sterilize heat liable liquids, serum, vitamins, hormones, solution of sugars or antibiotics used for the preparation of culture media.

28. TYPESOFFILTERSUSEDFORSTERILIZATIONPROCESSES
Asbestos filters Membrane filters Sintered glass filter

29. MEMBRANE FILTERS
• These are made up of cellulose esters or other polymers with specific spore size ratings.
• They retain particles or microbes larger than their pore size primarily by surface capture
(0.22um).

30. Chemical methods
for sterilization

31. Definition -: Chemical methods refer to the use of chemical
agents for sterilization. Several chemical agents are use as
antiseptic or disinfectants.

32. Howchemical agents kill microorganismsfor
sterilization? Protein coagulation
Disruption of cell membrane resulting in loss of
cellular contents
Substrate competition- A compound resembling the essential substrate of enzyme
misleads /diverts enzymes necessary for metabolism of cell, thus, causes death.
Removal of sulfhydryl groups that are essential
for the functioning of enzymes.

33. Typesofchemicalmethodsofsterilization
Liquids Gases
Alcohol Aldehyde Halogens Phenols Ethyleneoxide Formaldehyde gas
Methanol Formaldehyde Chlorine Lysol
Ethanol Glutaraldehyde Iodine Cresol

34. Liquids(liquid chemicals used as a sterilizing agent)

35. Alcohols
Methanol
 Usage - used for sterilizing cabinets & incubators.

 How methanol acts as a sterilizing agent?
It is effective against
fungal spores.
Ethanol
 Usage - used as skin antiseptics, 70% ethanol is mostly used as
sterilizing agent in laboratories.

 How ethanol acts as a sterilizing agent?
It denatures bacterial
protein but have no action
against spores.

36. Aldehydes
Formaldehyde
 Usage- usedto preservebiological specimens & as a preservative in vaccination.

 How it kills bacteria, fungi & including their spores ?
It is mainlyactiveagainst
the amino group of the
protein molecule.
Glutaraldehyde
 Usage – used to sterilize anesthetic tubes, face masks, plastic endotracheal tubes ,
polythene tubing etc.

 It is mostlyeffective against bacteriaTubercle bacilli, viruses&fungi.

37. Halogens
Iodine
 Usage- It is used as a disinfectant for skin.

 It is actively bactericidal against Tubercle bacilli, viruses & has
moderate action against spores.
Chlorine
 Usage - It is used as a disinfectant in water supplies,
swimming pools etc.


38. Phenols
Howphenolactsasasterilizingagent?
 The lethal effect of phenol is due to their capacity to cause cell membrane
damage, cell lysis & releasing their cell contents.
 Low conc. Of phenol precipitates proteins.
Examples-
 Lysol & Cresol

39. Gases ( Gases used as a sterilizing agent)

40. Ethyleneoxide
 It is a colorless liquid with a boiling point of 10.7*C.
 How it acts as a microbicide agent?
It is efficient in alkylating the amino, carboxyl, hydroxyl & sulfhydryl groups in protein
molecules.
It also reacts with DNA & RNA.
It diffuses through many porous materials & also it readily penetrates some
plastics.

41. Practicalapplicationsofethyleneoxide
-

It is used for sterilizing the following-
 Heart- lung machines
 Dental equipment
 Note- It is unsuitable for fumigating rooms because of its
explosive properties.

42. Thankyou