Microbial Control Methods

Question 1

Define sterilization

Answer 1

Destroys/Removes all viable microorganisms, including endospores

Question 2

Define disinfection

Answer 2

The destruction of vegetative mircoorganisms

Question 3

What are the conditions for autoclaving?

Answer 3

121°C, 15 psi, 15 mins

Question 4

How does autoclaving help to destroy all viable microorganisms?

Answer 4

The high pressure enables steam to reach a high temperature, increasing its heat content and killing power
Resulting in the denaturation and coagulation of proteins

Question 5

What are the limitations of autoclaving?

Answer 5

Not suitable for:

• heat-sensitive material and reagents
• moisture repelling substance
• substance that has to be kept dry

Question 6

How to prepare items for autoclaving?

Answer 6

Liquids:

• cap the bottles loosely
• fill it till its half full

Plastic containers with no lids:
- cover the containers with aluminium foil with no holes

Other glass/metal utensils:
Wrap in aluminium foil with no exposed edges

1 piece of autoclave tape on each item
Leave space between items

Question 7

How to validate the effectiveness of the autoclave process?

Answer 7

Use 2 biological indicator
1 acts as a control (placed outside)
Place the other in the autoclave
When the ampoule breaks, the medium would be able to mix with the endospores
The media colour of the one in the autoclave should remain purple, as the endospores are killed.
The media colour of the one placed outside should turn from purple to yellow

Question 8

What are the conditions for dry heat (oven)?

Answer 8

170°C, normal air pressure, 1 hr

160°C, under normal air pressure, 2 hr

Question 9

What are the conditions for flaming using a Bunsen burner?

Answer 9

1870°C

Metal should turn orange-red, indicating that it has been sufficiently heated and microbes would have been killed

Question 10

What are the limitations for dry heat (oven and flaming)?

Answer 10

Suitable for metals and heat resistant glass materials only

Question 11

What are the conditions for filtration?

Answer 11

The pore size of the filter should be 0.22ul (micrometre)

Question 12

What are the limitations for filtration?

Answer 12

Viruses that are smaller than 0.22ul will get filtered through
Pyrogens and endotoxins are not removed
Limited volume gets filtered

Question 13

What are the steps we need to take to carry out filtration?

Answer 13

1. Load the sample into the syringe
2. Prepare a sterile container to hold the filtrate
3. Attach the filter securely
4. Hold the assembled syringe and filter vertically, to wet the membrane evenly
5. Press the syringe plunger gently to push the sample through the filter
6. Change filter and repeat the above steps for the next sample

Question 14

When should we use ultraviolet radiation to disinfect?

Answer 14

When we want to disinfect the air, thin stream of liquid and solid surfaces

Question 15

When should we use 70% ethanol to disinfect?

Answer 15

When we want to disinfect solid surfaces and equipment

Question 16

When should we use bleach to disinfect?

Answer 16

When we want to disinfect biological liquid waste

1: 10 (v/v) dilution is used to disinfect general biological liquid waste
1: 15 (v/v) dilution is used to disinfect biological liquid waste containing a high organic load

Question 17

What are the limitations when using UV radiation?

Answer 17

Low penetrating power

Bacterial endospores can be eliminated only on longer exposure

Question 18

What are the limitation when using 70% ethanol?

Answer 18

Not suitable for disinfecting wounds, as it can cause protein coagulation
Cannot kill endospores (no matter what)

Question 19

What are the limitations when using bleach?

Answer 19

Corrosive
Light sensitive
Require more hours to kill endospores