Sterilization Methods

Question 1

How are the main sterilization methods classified?

Answer 1

Physical Agents
1) Heat
2) Radiation
3) Filtration

Chemical Agents

Question 2

What is the name of chemical antimicrobial agents that kill bacteria?

Answer 2

Bactericidal

Question 3

What is the name of chemical antimicrobial agents that inhibit the growth of bacteria?

Answer 3

Bacteriostatic

Question 4

What are disinfectants?

Answer 4

chemicals that are used for disinfection

Question 5

What should disinfectants be used on?

Answer 5

only on inanimate objects.

Question 6

What are antiseptics?

Answer 6

mild forms of disinfectants that are used externally on living tissues to kill microorganisms, e.g. on the surface of skin and mucous membranes.

Question 7

What should antiseptics be used on?

Answer 7

animate surfaces

Question 8

What is the importance of terilization and disinfection?

Answer 8

• laboratory safety
• patient safety
• microbiological test accuracy and validity

Question 9

What is sterilization?

Answer 9

The killing or removal of all microorganisms, including bacterial spores which are highly resistant.
- absolute term

Question 10

What is teh difference between disinfection and sterilization?

Answer 10

Disinfection is the killing of many, but not all microorganisms.
Sterilization is the killing of all microorganisms.

Question 11

What is disinfection?

Answer 11

• process of reduction of number of contaminating organisms to a level that cannot cause infection, i.e. pathogens must be killed.
• some organisms and bacterial spores may survive.

Question 12

What is the use of sterilization?

Answer 12

• Sterilization for Surgical Procedures
• Sterilization in Microbiological works

Question 13

What is the most effective and a rapid method of sterilization and disinfection?

Answer 13

HEAT
- excessive heat acts by coagulation of cell proteins.
- less heat interferes metabolic reactions.

Question 14

What are the two most common method used in the laboratory?

Answer 14

sterilization by hot air in hot air oven and sterilization by autoclaving.

Question 15

What are the different types of heat?

Answer 15

1) moist heat
2) dry heat

Question 16

What is the function of sterilization by dry heat?

Answer 16

• denaturation and coagulation of protein,
• breakage of DNA strands,
• loss of functional integrity of cell membrane.

Question 17

What is the function of sterilization by moist heat?

Answer 17

Boiling.
- 100°C for 30 minutes
- done in a water bath.

Syringes, rubber goods and surgical instruments
may be sterilized by this method.

• All bacteria and certain spores are killed.
• It leads to disinfection.

2. Steaming.
- (100°C) is more effective
- Bacteria are more susceptible to moist heat,
- Steam has more penetrating power, and
- Steam has more sterilizing power as more
heat is given up during condensation.
- It is ideally suitable for sterilizing media which
may be damaged at a temperature higher than
100°C.

Question 18

What is better dry or moist heat?

Answer 18

moist –> steaming

Question 19

What is pasteurization? Why is it used?

Answer 19

• heating of milk to kill pathogenic bacteria that may be present in milk without changing colour, flavour and nutritive value of the milk.
• Mycobacterium bovis, Salmonella species,
  Escherichia coli and Brucella species may be
  present in milk.
• It does not sterilize the milk as many living
  organisms including spores are not destroyed..

Question 20

What are the methods of pasturization?

Answer 20

Flash Method.
- high temperature- short time method
- 72°C for 15 seconds.

Holding Method.
- between 63°C and 66°C for 30 minutes.
- immediately cooled to below 10 degrees.

Question 21

What is inspissation? Where is it completed?

Answer 21

• stiffening of protein without coagulation as the temperature is below coagulation temperature.
• 75°C - 80°C.
• media containing serum or egg is sterilized by
  heating for 3 successive days.
• done in a ‘Serum Inspissator’.

Question 22

What is tyndallization?

Answer 22

fractional sterilization
- used for heat labile media (containing sugar, milk, gelatin)

Question 23

When are spores usually destroyed?

Answer 23

Spores, if any, germinate to vegetative bacteria during incubation and are destroyed during steaming on second and third day.

Question 24

What is autoclaving?

Answer 24

• sterilization is done by steam under pressure.
• 100°C+

Question 25

What are the methods of dry heating?

Answer 25

Red Heat.
- Wire loops used in microbiology laboratory are sterilized by heating to ‘red’ in bunsen burner or spirit lamp flame.
- Temperature is above 100°C. It leads to
sterilization.

Flaming.
- The article is passed through flame without allowing it to become red hot, e.g. scalpel.
- Temperature is not high to cause sterilization.

Question 26

How are things sterilized by hot air?

Answer 26

Hot Air Oven (Sterilizer):
- most common method
- 1h 160°C
- spores are killed at this temperature

Question 27

What microrganism’s according to the innate resistance?

Answer 27

1. Prions (the most resistant)
2. Spores
3. Tubercle bacilli
4. Non enveloped viruses
5. Fungi
6. vegetative bacteria
7. Enveloped viruses such as HBV, HIV

Question 28

How are things sterilized by radiation?

Answer 28

• ionizing radiation rays emitted from radioactive cobalt 60 or beta rays emitted from electron accelerators.
• High penetrating power.
• Used for plastic syringes, catheters, gloves,
  surgical sutures.

Question 29

How are things sterilized by filtration?

Answer 29

fluid filters:
- vacuum or seitz filter
- millipore (membrane) filter
- syringe filter

air filters

Question 30

What is plasma? What is it used for? Is it toxic?

Answer 30

• any gas which is formed of ions, electrons, neutral particles,
• used for surgical instruments mainly those
  with narrow lumen such as arthroscopic and
  laparoscopes.
• non toxic.