Disinfection & Sterilisation (L19&20)

Question 1

Define disinfection

Answer 1

Process by which the number of microorganisms are reduced to a level that is considered safe

• some bacteria, spores & viruses remain

Question 2

What does cleaning do? (x2)

Answer 2

1. Reduces the bioburden (e.g. blood/skin), making everything else more effective after that
2. Removes chemical traces

Question 3

How to clean? (x3)

Answer 3

1. manual / automated machine
2. hot water and detergent, rinse thoroughly and dry
3. dry via disposable towels or automa

Question 4

3 Sources of heat for disinfection

Answer 4

1. Pasteurisation at 63deg for 30min or 72deg for 20 min
2. Boiling water for 10min
3. Washing and rinsing from 70deg to 90 deg

Question 5

What does ultrasound utilise and what are its functions?

Answer 5

utilise HIGH FREQUENCY SOUND WAVES; Remove dirt also disrupt cells, membranes. they are used in preparation of material prior to autoclaving (e.g. burs)

Question 6

Compare between disinfectants and antiseptics

Answer 6

Both are chemical methods of disinfection.

Disinfectants are for use on inanimate objects while antiseptics are for use on living tissue

Question 7

What can be used to reduce microbes on skin and mucous membranes? (X4)

Answer 7

1 Alcohols (70% isopropanol or 70% ethyl-alcohol)
2 Cetrimide ("Savlon")
3 Chlorhexidine (Bisguanides)
4 Iodine

Question 8

Mode of action of alcohols (x5)

Answer 8

1. Requires wet contact for 3mins
2. Kills bacteria rapidly (30secs on dry surface)
3. Inactive against spores and fungi
4. Evaporates, flammable and inactivated by organic material
5. Used as skin antiseptic before injection

Question 9

What can be used to reduce microbes on inanimate objects? (x3)

Answer 9

1 Hypochlorites (eg NaOCl)
2 Phenols
3 Alcohols

Question 10

Briefly describe Cetrimide

Answer 10

It is a low level disinfectant made up of quaternary ammonium compounds, containing cationic surface active detergents.

It is inactivated by many substances including anionic detergents, soap and water.

Question 11

How does the cationic surface active detergents help in reducing microbes?

Answer 11

Cationic charge is key to disruption of membrane because of the interaction with the phospholipid membrane, allowing it to interact/penetrate membrane.

Question 12

Name two substances that inactivate staphylococci but are not so active against other bacteria

Answer 12

1. Chlorhexidine

2. Cetrimide

Question 13

Hypochlorites are often used for impression disinfection. What solutions should be used for:

a) Impression with visible blood contamination
b) Impression without blood contamination

Answer 13

a) “Strong” hypochlorite 1% solution, expose for 2 mins

b) “Weak” hypochlorite 0.1 solution, expose for 10mins

Question 14

Which disinfectant is effective for bacterial spores?

Answer 14

Hypochlorite

Question 15

Define sterilisation

Answer 15

The process by which all micro-organisms are killed or removed to render the object incapable of causing infection

Question 16

List 4 methods of sterilisation

Answer 16

1. Heat
2. Chemical
3. Radiation
4. Filtration

Question 17

How does moist heat work?

Answer 17

It kills by coagulating and denaturing enzymes and structural proteins

Question 18

Name 2 methods of chemical sterilisation

Answer 18

1. Formaldehyde vapour

2. 2% Gluteraldehyde

Question 19

List the symptoms of vCJD (x7)

Answer 19

1. Average age 28
2. Progressive dementia
3. Sensory symptoms
4. Unsteadiness
5. Involuntary movements
6. Immobile and mute
7. Death in

Question 20

Compare the variant CJD (vCJD) with sporadic CJD (sCJD) (x2)

Answer 20

1. Average age affected - 28 VS 65

2. Death in less than 14 months VS 4.5 months

Question 21

Name a prion based disease

Answer 21

Creutzfeldt-Jakob disease (CJD) (a fatal human neurodegenerative condition)

Question 22

How is CJD transmited

Answer 22

person-to-person spread by contaminated surgical instruments that have not been cleaned/disinfected