Sterilization is a process that kills all microorganisms through various means like heat, chemicals, irradiation, etc. Dry heat sterilization uses high temperatures without moisture to destroy microbes. Common dry heat methods include hot air ovens, flaming, and incineration. Hot air ovens circulate hot air above 170°C for at least 60 minutes to ensure sterilization through protein denaturation and cell membrane disruption. Flaming uses the flame of a Bunsen burner to heat items red hot above 250°C, while incineration reaches temperatures over 870°C to sterilize through complete burning. Dry heat requires higher temperatures and longer times than wet heat sterilization methods.

1. An Assignment on
Sterilization by
Dry Heat
Submitted by
Roll:-14308
Reg:-1086
Date of Submission:-18/03/21
Submitted to
Mr Mohammad Kamal Hossain
Assistant professor
Department of Pharmacy,
University of Science and Technology
Chittagong (USTC)
Department of Pharmacy
Course Name: Applied Microbiology
Course No:-PHR-308

2. Sterilization refers to any process that removes, kills, or deactivates all forms
of life (in particular referring to microorganisms such
as fungi, bacteria, spores, unicellular eukaryotic organisms such as Plasmodium,
etc.) and other biological agents like prions present in a specific surface, object or
fluid, for example food or biological culture media. Sterilization can be achieved
through various means, including heat, chemicals, irradiation, high pressure,
and filtration. Sterilization is distinct from disinfection, sanitization,
and pasteurization, in that those methods reduce rather than eliminate all forms of
life and biological agents present. After sterilization, an object is referred to as
being sterile or aseptic.
Importance of sterilization:-
To prevent contamination in sterile products
To prevent transmission of pathogenic microorganisms which are
responsible for causing disease in plants, animals and human beings
To prevent decomposition and spoilage of food and food products
To prevent the contamination of unwanted microbes in pure cultures
and other microbiology experiments performed for research studies
To prevent unwanted microbial contamination in antibiotic,
enzyme, vitamins, fermentation and other industries process
To prevent contamination in aseptic areas/instruments which are used for
the preparation of sterile dosage forms and sterility testing.
Introduction

3. Method of sterilization:-
Physical Method:-
Sterilization
Physical Method Chemical Method
Physical Method
Heat
Sterilization
Dry Heat
Moist Heat
Filtration Radiation

4. Dry Heat:-
Microorganisms are capable of causing infection are constantly present in
the external environment and on the human body.
Microorganisms are responsible for contamination and infection.
The aim of sterilization is to remove or destroy the microorganisms from
materials or from surfaces.
 Denaturation of proteins
 Interference with protein synthesis
 Interruption of DNA synthesis
 Oxidative damage of cell
 Disruption of cell membranes
Dry Heat
Flaming Incinaration Hot Air Oven
Why we need Sterilization
How can microorganisms be killed

5. Fig;-Protein Denaturation
 Contact time
 Physico-chemical environment (e.g. pH)
 Presence of organic material
 Temperature
 Type of microorganism
 Number of microorganisms
 Material composition
• Heat is the most reliable and rapid method of sterilization
Mechanism:
Protein denaturation
oxidative damage
Factors that influence efficacy of disinfection/sterilization
DRY HEAT STERILIZATION

6. Toxic effect of elevated levels of electrolytes.
 Time required for sterilization is inversely proportional to the temperature
of exposure. This can be expressed as thermal death time, which is the
minimum time required to kill a suspension of microorganisms at a
temperature and specific conditions.
• Hot air ovens are electrical devices used in sterilization.
• The oven uses dry heat to sterilize articles.
• Generally, they can be operated from 50 to 300 C (122 to 572 F) .
• There is a thermostat controlling the temperature.
• This is the most widely used method of sterilization by dry heat.
• Items:glassware, forceps, scissors, scalpels, all-glass syringes,
swabs, liquid paraffin, dusting powder, fats, grease.
• (Materials should be properly arranged to allow free circulation of air)
Hot Air Oven

7. Fig:-Hot Air Oven

8. Component of Hot Air Oven:-
 An insulated chamber surrounded by an outer case containing electric
heters.
 A fan to ensure even distribution of air
 Shelves
 Thermocouples
 Temperature
 Door locking controls.
Precautions:
Should not be overloaded.
Arranged in a manner which allows free circulation of air.
Material to be sterilized should be perfectly dry.
Test tubes, flasks etc. should be fitted with cotton plugs.
Paper wrapping of the items should be done.
Rubber materials and inflammable materials should not be kept
inside.
The oven must be allowed to cool for two hours before opening, since
glassware may crack by sudden cooling.
Sterilization control:
Effectiveness of sterilization can be monitored by:
 Biological indicators: — Paper strips with 106 Spores of Clostridium tetani
or Bacillus subtilis placed with other material. Later culture the strips in
thioglycollate broth at 370C for 5 days. Growth indicates failure
of sterilization.
 Thermocouples: records the temperature by a potentiometer.
 Browne's tube: contains a heat sensitive dye which turns green after being
exposed to 1600C for 60 minutes or 1500C for 115 minutes.

9. Advantages:-
• They do not require water and there is not much pressure build up within
the oven, unlike an autoclave, making them safer to work with.
• Suitable and easy to be use in a laboratory environment.
• They are much smaller than autoclaves but can still be as effective.
Disadvantages:
• long heating time, high temperature.
• As they use dry heat instead of moist heat, some organisms like prions, may
not be killed by them every time.
 Items are held in the flame of Bunsen burner either for long time or short
time
 longer time exposure in flame till they become red hot(250-3000C)
 done for inoculating wires or loops, tips of forceps, etc.
 Shorter period of time without allowing the items to become red hot: done
for fragile items ,e.g. glass slides, mouth of test tubes and flask.
Temperature (c) Time(in minutes)
170 60
160 120
150 150
140 180
Flamming

10. Fig:-Flamming
 It is used for disposal of biomedical waste materials.
 Materials are reduced to ash by burning.
 It burns( sterilize) the anatomical waste , animal carcasses
,pathological waste and contaminated cloths by providing a very high
temperature(870- 1,2000C).
Incinaration

11. Fig:- Incinaration
:
Sterilization is a process or killing all microorganisms (including,spores) on
or in a material or object.
The factorsüat determine the type of sterilization or disinfecting process to
be used include time, temperature ,stage of growth of the organism ,nature
of the medium in which the organism is suspended (air, gas ,liquid) and the
number of organism present.
Sterilization and disinfection can be achieved by using heat, filtration,
chemical or radiation etc.
Overall, heat is the best means of sterilization, but other methods are used
for heat labile objects.
Summery

12. Dry heat requires more time than wet heat to kill organisms ,boiling kills
most vegetative cells but not bacterial spores & pressure cookers
&autoclaves achieve sterilization
 Remington. The science and practice of pharmacy, 21st edition volume-1,
Page no.776-801.
 Ananthanarayan ,Paniker's. Textbook of microbiology, (8th edition) page
no.30-38.
 Tortora, Microbiology an introduction. (9th edition) page no. 188-197.
 Purohit S S, Microbiology fundamentals and applications. (6th
edition) page no.354-366.
 Michael J. Pelzar, Microbiology.(5th
edition).McGraw Hill, page no.474-
491.
 Hugo and Russell 's, Pharmaceutical Microbiology. page no.336-345.
 Dr. R. C. Dubey, Dr. D. K. Maheshwari, A textbook of microbiology. page
no. 110.546-549.
References