Mechanical Means -scrubbing -filtration -sedimentation

1. PHYSICAL AGENTS
OF STERILIZATION

2. Mechanical Means
• Mechanical means is used to achieve a
high degree of cleanliness and microbe
removal, but not to accomplish sterilization.
• Mechanical means include the following:
- Scrubbing
- Filtration
- Sedimentation

3. Mechanical Means
• Scrubbing
- both mechanical and chemical
- usually done using soap and water
- removes microogranisms mechanically
while the soap acts upon them chemically.

4. • Filtration
- made of filter papers, unglazed porcelain,
diatomaceous earth, compressed
asbestos, sintered glass and cellulose
membranes
- mechanical removal of bacteria by passing
a liquid with bacteria through a material
with pores so small that the bacteria are
held back
- widely used for sterilizing liquids and
culture media
- widely used in pharmaceutical laboratories

5. •Sedimentation
- process by which bacteria and other
particles suspended in a liquid coagulate
and settle to the bottom.

6. Heating Procedures
• Heat is the most widely used and most
effective means of sterilization.
• The time required to kill all
microorganisms at a given temperature is
known as the thermal death time.
• The temperature that will kill a species of
microorganism in 10 minutes at pH 7 is
known as the thermal death point.

7. • Dry heat
- used primarily for sterilizing objects made
of glass, metal, and substances that are
damaged by moisture.
- kills by oxidation
- kills vegetative bacteria at 120ºC to 130ºC
in 1 1/2 hours.
- kills spore formers at 160ºC in 15 to 20
mins.

8. • Moist heat
- kills by coagulation of the protein in the
microorganism
- kills all vegetative bacteria and most
spores at 120ºC in 15 mins.
- applied in several ways:
- boiling
- steam under pressure/autoclaving
- intermittent sterilization tindallization
- pasteurization

9. Moist Heat
• Boiling
- kills vegetative forms of pathogenic
microorganisms in 5 minutes or less.
- 2% sodium carbonate hastens destruction
of spores/prevents rusting of instruments

10. Moist Heat
• Steam under Pressure
( autoclaving )
- effective means of sterilization through the
use of autoclave
- autoclave kills organisms and spores in 15
to 45 mins
- yields heat by condensing back into water

11. Moist Heat
• Intermittent Sterilization
Tyndallization
- free flowing steam at atmosphere pressure
for 30 mins for 3 consecutive days
- vaccines: 55ºC to 60ºC for 1 hour
5 to 6 consecutive days

12. Moist Heat
• Pasteurization
- efficient method for heating milk and other
liquids to destroy undesirable
microorganism without changing its
composition and food value.
- beta rays

13. Moist Heat
• Pasteurization
- beta rays sterilizes sutures and plastic
tubings; used for the treatment of sewage
and waste water
- lasers are used to sterilize medical
intruments, clear the air in operating
rooms and pick organisms off a wound
surface
- ultrasonics are mechanical vibrations

14. Other Physical Means
• Natural Methods
- drying is the removal of water from the
material
sunlight is the inhibitor and destructive
acyion on microbes; used in home-drying
food preservation

15. Other Physical Means
• UV Radiation
- used to prevent airborne spread of
disease-producing agents in public places,
microbial laboratories, pharmaeutical
laboratories and animal quarters.

16. Other Physical Means
• X-rays and Radiations
- lethal to microbes

17. Other Physical Means
• Fluorescent Dyes
- methylene blue, rose bengal and eosin are
lethal bacteria and viruses when in contact
with strong visible light