Disinfectants

Question 1

Give 4 factors that effect environmental persistence if pathogens

Answer 1

• General cleaning routine
• Surface structures e.g. crevices
• Surface characteristics i.e. absorbant, soft, smooth
• Weather outside , soil pH faecal contamination

Question 2

Describe thermal inactivation

Answer 2

o	E.g. autoclave (121 degrees for 15 mins)
o	Decontamination runs
o	Prions (134 degrees repeat cycles)

Question 3

What temperature is required to sterilize endospores

Answer 3

121 degrees for 15 minutes

Question 4

What temperature is required to sterilize canine parvovirus (enveloped)

Answer 4

100 degrees for 10 seconds

Question 5

What temperature is required to sterilize Most vegetative bacteria

Answer 5

85 degrees for 10 seconds

Question 6

What temperature is required to sterilize many of the public health vegetative bacteria

Answer 6

72 degrees for 20 seconds

Question 7

What temperature is required to sterilize canine distemper virus/mycoplasma

Answer 7

60 degrees for 2 minutes

Question 8

Describe the process and effects of pasteurisation

Answer 8

• Rapidly heating and then rapidly cooling food
Not sterilisation and does not kill all microorganisms in food
• Reduces the number of sensitive viable pathogens
• 90% effective against vegetative bacteria

Question 9

Define disinfection

Answer 9

• Disinfection  destruction of microorganisms by physical or chemical methods on surfaces of objects

Question 10

Define antisepsis

Answer 10

ntisepsis  Destruction of microorganisms on tissues by chemicals which are non toxic and non irritating to the tissue

Question 11

Describe the ideal chemical disinfectant

Answer 11

• Broad activity, absence of irritancy, toxicity etc
• Long shelf life, stable
• Soluble in water and compatible with a wide range of other chemicals
• Active in organic matter and over a range of temperatures
• Non corrosive to metal and non polluting/biodegradeable

Question 12

Describe prions

Answer 12

• Not living?, Already denatured?
• Highly resistant
• So poor activity

Question 13

Describe the mode of action, main uses and problems of acids as disinfectants

Answer 13

Mode of Action
- function related to pH 
- destroys nucleic acid  bonds and precipitate proteins
Problems 
- Caustic and fumes 
- Reactive and can damage surfaces
Main uses 
- HCl can destroy endospores
- Clean out alkaline deposits in machinery such as milking machines

Question 14

Describe the mode of action, main uses and problems of alcohols as disinfectants

Answer 14

Mode of Action
- Denatures proteins causing membrane damage
- Broad action (but requires water)
- Rapid activity against vegetative bacteria
Problems
• Flammable
• Limited activity in presence of organic material
Benefits
• Evaporates quickly leaving no residue
• Can be used or combined with other anti microbial compounds
• Convenient (is this a good reason?)

Question 15

Describe the mode of action, main uses and problems of alkalis as disinfectants

Answer 15

Action
- Saponifying lipids in cell membranes and envelopes (increased activity with temperature)
Problems
• Caustic and fumes
• Cause corrosion
• Care: some react when being violently added to water never put water directly onto dry alkalis (exothermic)
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