dry and wet sterilization

1. DRY AND WET
STERILIZATION
K. ACHYUTH ACHARI
2022-11-113
Msc plant pathology
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2. INTRODUCTION :
Sterilization is a process of removal or killing of all forms of microbial life including
spores
From an object, surface, medium or environment without spoiling its nature
However several factors influence the effectiveness of sterilization process like the
concentration of antimicrobial agents, time and temperature of exposure, size of
population, type of contaminating microbes etc.
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4. PHYSICAL METHODS :
1.Heat
a) Dry heat: Hot air oven etc
b) Wet heat: Autoclave etc
2.Radiation
3.Filtration
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5. DRY HEAT STERILIZATION :
• Simplest method is exposing the item to be sterilized to the naked flame e.g.
Bunsen burner- for sterilizing bacteriological loops, knives, blades
• Heat sterilization is the most widely used and reliable method of sterilization,
involving destruction of enzymes and other essential cell constituents
• It employs higher temperatures in the range of 160-180°C and requires exposures
time up to 2 hours, depending upon the temperature employed
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6. Incineration
Red heat
Flaming
Hot air oven
Incineration Flamming
Red heat Hot air oven
Dry heat
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7. Red heat:
• Sterilization is done by holding materials in a bunsen
burner Flame until they become red hot. It is used to
sterilize Inoculation straight wires &wire loops, tips of
forceps and Spatulas
 Flaming:
• This is a method of passing article over a flame, but not
Heating it to redness. It is used to sterilize mouth of test
& flasks, used scalpels, glass slides & cover slips
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8. Incineration :
• Incineration is the process of sterilization along with a
significant reduction in the volume of the wastes.
• It is usually conducted during the final disposal of the
hospital or other residues. The scraps are heated till they
become ash which is then disposed of later.
• This process is conducted in a device called incinerator.
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9.  HOT AIR OVEN :
• It sterilizes the objects that cannot be sterilized by moist heat.
• It uses the principle of conduction in which the heat is first absorbed by the outer
surface and is then passed into the inner layer.
• A hot air oven consists of an insulated chamber that contains a fan, thermocouples,
temperature sensor, shelves and door locking controls.
• The commonly-used temperatures and time that hot air ovens need to sterilize materials
are 170°C for 30 minutes, 160°C for 60 minutes, and 150°C for 150 minutes.
• These ovens have applications in the sterilization of glassware, petri plates, and even
powder samples
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11. Advantages :
 effective method, as dry heat by conduction reaches all surfaces of instrument, even for instruments
that can’t be disassembled
 Good penetrability& Non-corrosive nature
 Leaves no chemical residue
Disadvantages
 Plastic and rubber items can't be dry heat sterilized because temp used (160-170°c) are too high for
these materials
 Dry heat penetrates materials slowly and unevenly
 Requires continuous source of electricity
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12. WET STERILIZATION :
• Moist heat sterilization is one of the most effective methods of sterilization
where the steam under pressure acts as a bactericidal agent.
• In this method, the microorganisms are killed by coagulating their proteins,
and this method is much more effective than dry heat sterilization where
microbes are killed through oxidation.
• It is used for heat sensitive materials and materials through which steam is
permeable.
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13. • Pastuerization
<1000c
• Boiling
• Tyndalization
1000c
• Autoclave
>1000c
Temperatures
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14. AUTOCLAVE :
Moist heat sterilization above 100°C involves
sterilization by steam under pressure.
• When pressure is increased in a closed vessel the
temperature increases proportionately i.e. For
about 15 pounds of pressure per square inch (psi)
the rise to 121°C.
• This pressure and temperature is kept constant
for 20 minutes during autoclaving.
•It is sufficient to kill all the vegetative forms and
spores of the organisms 14

15. Advantages :
 Useful for materials that can not withstand high temp
 Sterilize media
Disadvantages :
 Temp sensitive media, antibiotics, etc cannot be sterilized
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16. REFERENCES :
• Ferdowsi, A., Ferdosi, M., And mehrani, M.J., 2013. Incineration or autoclave? A
comparative study in isfahan hospitals waste management system
(2010). Materia socio-medica, 25(1), p.48
• Https://study.Com/learn/lesson/moist-heat-sterilization-autoclave-method-uses-
disadvantages.Html
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