IA. General microbiology | 5. Sterilization

Question 1

I. Sterilization
1. What is sterilization?

Answer 1

• killing procedure of any kind of germs ……..
• inactivation (killing) of all forms of microbial life (pathogenic microbes and spores)

Question 2

I. Sterilization
2. What is sterile?

Answer 2

Sterile: an object that is free of all living organisms

Question 3

I. Sterilization
3. How can sterile be achieved?

Answer 3

Can be achieved via application of heat, chemicals, iradiation, high pressure and filtration

Question 4

I. Sterilization
4. What is the aim of sterilization?

Answer 4

Complete removal or destruction of all forms of microbial life including bacterial spores

Question 5

I. Sterilization
5A. What is decimal time (D)?

Answer 5

• Decimal time (D): time needed to reduce the initial number (N0) to one tenth of its original value
• Number of microorganisms (N) after sterilization is given by:

Question 6

I. Sterilization
5B. What are the features of D?

Answer 6

D varies with temperature, type of organism, water activity, pH, etc.
■ D becomes considerably shorter with increased temperature → high temperature will reduce the N0 faster than low temperature.

Question 7

I. Sterilization
6. What are the 5 applications of sterilization?

Answer 7

○ Sterilization of medical instrumentations
○ Annihilation of infectious waste
○ Sterilisation of injectable medications
○ Skin disinfection
○ Food safety

Question 8

II. Methods of Sterilization
1. Classification of methods of sterilization

Answer 8

Question 9

II. Methods of Sterilization
2. Classification of physical methods

Answer 9

Question 10

II. Methods of Sterilization
3. Classification of chemical methods

Answer 10

Question 11

II. Methods of Sterilization
4. Classification of mechanical method

Answer 11

Question 12

II. Methods of Sterilization - Physical method (Heat)
1. What are the features of flaming (dry heat) method?

Answer 12

○ Instruments are held in flame until they become red hot
○ Incinerating biological waste from hospitals and laboratories
○ Use: inoculation loop, inoculation needle, scalpels, mouth of test
tube, top of forceps

Question 13

II. Methods of Sterilization - Physical method (Heat)
2. What are the features of hot air oven (dry heat) method?

Answer 13

Hot air oven (dry heat) – most widely used method
○ Heating at atmospheric pressure and often use a fan to obtain uniform temperature by circulation
○ 1hr→ 180°C ;2hr →160°C; 3hrs→140°C
○ Use: laboratory glassware, ceramics, surgical instruments
without sharp edges, powders
tube, top of forceps

Question 14

II. Methods of Sterilization - Physical method (Heat)
3A. What are the features of utoclaving (moist heat) or steam sterilizer?

Answer 14

• Insulated pressure chamber in which saturated steam is used to elevate the temperature
• Denaturation and coagulation of microbial protein occur during exposure to the high temperature of the steam
• 121°C at +1atm overpressure for 20-30mins
• 134°C at +2atm overpressure for 10mins

Question 15

II. Methods of Sterilization - Physical method (Heat)
3B. Why is autoclaving (moist heat) or steam sterilizer more effective than DRY HEAT?

Answer 15

• More rapid, even penetration
• Better bactericidal/virucidal effect
• Short efficient cycle time

Question 16

II. Methods of Sterilization - Physical method (Heat)
3C. What is the use of autoclaving (moist heat) or steam sterilizer?

Answer 16

Microbiological media, solutions, glasswate, surgical instruments, cotton items, items made of autoclavable rubber, swabs, tissue paper

Question 17

II. Methods of Sterilization - Physical method (Heat)
3D. Give steps of Autoclave sterilization methods to destroy prions (protein only)?

Answer 17

1. 1N NaOH 2hrs or 2N NaOH 1hrs
2. +2atm overpressure, 134°C, 1hrs
3. Repeat whole process

Question 18

II. Methods of Sterilization
4. What are the 3 factors in sterilization testing?

Answer 18

1. Physical parameters – time, temperature, pressure
2. Chemical indicators – exposition to heat - colour change (paper strips)
3. Biological indicators – if good, bacteria will fail to grow (geobacillus stearothermophilus spores)

Question 19

II. Methods of Sterilization - Physical method - Radiation
5A. What are the 2 types of radiation method?

Answer 19

1. UV light
2. Gamma sterilization

Question 20

II. Methods of Sterilization - Physical method - Radiation
5B. What are the features of “UV Light” method?

Answer 20

• Germicidal lamps: short distance → surface, air, biological safety
• Cabinets, laminar flow cabinet → totally germfree
• DNA mutates and breaks down → damage the structure and function of nucleic acid → cell death
• Can cause damage to human cells

Question 21

II. Methods of Sterilization - Physical method - Radiation
5C1. What are the features of “Gamma sterilization” method?

Answer 21

• Coblat 60 radiation to kill microorganisms
• Produce electron disruptions (ionization) in any material that it encounters
• Living organism – disruptions result in damage to the DNA and other cellular structures – could cause death in organisms
• Can damage human cells – risk of cancer
• Use: single use, individually packaged, heat sensitive instruments (plastics, swabs catheters, infusion set, glove syringe

Question 22

II. Methods of Sterilization - Physical method - Radiation
5C2. What is the use of “Gamma sterilization” method?

Answer 22

Use: single use, individually packaged, heat sensitive instruments (plastics, swabs catheters, infusion set, glove syringe

Question 23

II. Methods of Sterilization - Chemical method
6A. What are the 2 chemical method?

Answer 23

Gas sterilization
Plasma sterilization

Question 24

II. Methods of Sterilization - Chemical method
6B. What are the features of gas sterilization?

Answer 24

• Ethylene oxide, β-propiolactone, ortho-phthalaldehyde (OPA),formaldehyde
• Highly penetrative, non-corrosive agents
• Against: bacteria, spores and viruses
• Destroys microorganism by alkylation; and causes denaturation of nucleic acid
• Use: single use, heat-sensitive, medical devices (prosthetic heart valves and plastic catheters and textiles)

Question 25

II. Methods of Sterilization - Chemical method 6C. What are the features of Plasma sterilization?

Answer 25

- Low-temp (~46°C), low humidity sterilization with plasma state hydrogen peroxide created using an electromagnetic field - Gas like plasma -- cloud of ions, electrons, neutral atomic particles -- created free radicals and biologically active particles destroy microorganisms. - Electromagnetic field is turned off -- hydrogen peroxide decays to water and oxygen - Use: metallic, non-metallic, wet/heat - sensitive instruments - At the end of the procedure there will be H2O, O2 & non toxic products

Question 26

II. Methods of Sterilization 7A. What are the features of Filtration method, a mechanical method?

Answer 26

Aqueous liquids, including solutions of heat-labile and irradiation-sensitive substances, may be sterilized by forced passage through a filter of porosity small enough to retain any microorganisms contained in them

Question 27

II. Methods of Sterilization - Filtration 7B. What are the 4 types of filters in filtration?

Answer 27

- Candle filters - Asbestos filters - Sintered glass filters - Membrane filters

Question 28

II. Methods of Sterilization - Filtration 7C. What are the features of candle filters?

Answer 28

purification of water for industrial purpose

Question 29

II. Methods of Sterilization - Filtration 7D. What are the features of Asbestos filters?

Answer 29

- disposable, single use discs. - High absorbing capacity.

Question 30

II. Methods of Sterilization - Filtration 7E. What are the features of . Sintered glass filters?

Answer 30

low absorptive property. Brittle and expensive.

Question 31

II. Methods of Sterilization - Filtration 7F. What are the features of Membrane filters?

Answer 31

- routinely used in purification and analysis. - The use of graded pore size: 0.2-0.4μm.