Sterilisation and Disinfection

Question 1

Define Sterilisation

Answer 1

The removal or inactivation of all micro-organisms from an article including viruses, bacteria and their spores’ and fungi and their spores

Question 2

Define Disinfection

Answer 2

Removal or inactivation of some micro-organisms from an article

Question 3

Define Antiseptic

Answer 3

Substance which destroys or inhibits the growth of micro-organisms - can be applied to living tissue

Question 4

Define Asepsis

Answer 4

State of being free from living organisms

Question 5

Define cleaning

Answer 5

Soil removing process - removes high proportion of micro-organisms present, usually prior to disinfection/sterilisation

Question 6

What are the 4 main methods of sterilisation

Answer 6

• Heat
• Irradiation
• Gas
• Filtration

Question 7

What are some influencing factors that affect sterilisation by heat

Answer 7

• Temp
• Time
• Number of organisms
• Species and spore-forming ability of the micro-organisms
• Nature of contaminated materials

Question 8

Is moist heat or dry heat better for sterilisation

Answer 8

Moist heat

Question 9

What are the conditions required to use moist heat for sterilisation

Answer 9

• Temp>100C
• Raising pressure of steam in pressure vessel (Autoclave)
• Steam must be saturated and dry must not contain water droplets

Question 10

What are different methods to apply dry heat sterilisation

Answer 10

• Incineration
• Red Heat
• Flaming
• Hot Air Steriliser
• Microwave Ovens

Question 11

When can you use hot air sterilisers

Answer 11

For materials that can withstand high temps for prolonged times and are likely to be affected by contact with steam

Question 12

What occurs in the red heat sterilisation method

Answer 12

Points of forces held in flame

Question 13

What temps and times are the minimums for dry heat sterilisation

Answer 13

160C - 60mins
170C - 40mins
180C - 20 mins

Question 14

What temps, pressures (in lb/in^2) and times are the minimums for dry heat sterilisation

Answer 14

121C - 15lb/in^2 - 15 mins
126 - 20lb/in^2 - 10 mins
134 - 30lb/in^2 - 3 mins

Question 15

How is Irradiation sterilisation carried out

Answer 15

• Ionising radiation including gamma rays, x rays and accelerated electrons

Question 16

What is irradiation often used for

Answer 16

Commercial sterilisation of single use items e.g. plastic straws

Question 17

Describe an example of how Gaseous sterilisation can be carried out

Answer 17

Ethylene oxide - highly penetrative and non-corrosive - used for commercial sterilisation of single use items

Question 18

Describe filtration sterilisation

Answer 18

Useful to exclude bacteria from fluids - 0.22um. pore size filter, excludes more bacteria but most viruses can pass

Question 19

What are sterilisation indicators

Answer 19

Used to determine whether sterilisation has occurred e.g. inside autoclave

Question 20

Describe how biological sterilisation indicators work

Answer 20

Usually cultures of Bacillus spp - after use the strips are cultured in media and any growth is indicative of sterilisation failure

Question 21

Name some non-biological examples of sterilisation indicators

Answer 21

• Externally calibrated thermocouple linked to a time monitor
• Autoclave tape and Browne’s tubes show apparatus show apparatus reached correct temp
• TST indicator strips (temp., steam, time)

Question 22

What are the 5 main methods for disinfection

Answer 22

1. Moist Heat
2. Ultraviolet Radiation
3. Gases
4. Filtration
5. Chemicals

Question 23

Describe the basic features of the moist heat disinfection method

Answer 23

• First choice
• No toxic residues
• 70-80C for a few mins kills most
• NB - boiling water won’t sterilise surgical instruments

Question 24

Describe the basic features of the ultraviolet radiation disinfection method

Answer 24

• Poor penetrating power

- Mercury lamps used in treatment of air, water and surfaces

Question 25

Name a gas used for gaseous disinfection and what this method would be used for

Answer 25

- e.g. formaldehyde gas - used for rooms and complex heat sensitive equipment

Question 26

Where is the filtration disinfection method used

Answer 26

Widely applied in the removal of micro-organisms to critical sites e.g. operating theatres

Question 27

What affects the activity of chemical disinfectants

Answer 27

- Concentration - No., type and location of micro-organisms - Temp and pH of treatment - Presence of extraneous material e.g. organic substances

Question 28

What classes of disinfectants are there

Answer 28

- Alcohols - Aldehydes - Biguanides - Halogens - Phenolics - Peroxygenated compounds - Surface-active agents

Question 29

Name some alcohol disinfectants

Answer 29

- Isopropanol | - Ethanol

Question 30

Name some aldehyde disinfectants and when are these used

Answer 30

Glutaraldehyde | Used for equipment that cannot be sterilised or disinfected by heat - broad spectrum of activity

Question 31

Name a Biguanide disinfectant and when are these used

Answer 31

Chlorhexidine | Used for disinfection of skin and mucous membranes

Question 32

Name some types of halogen disinfectant

Answer 32

Hypochlorites and iodine containing complexes (iodophors and povidone iodine)

Question 33

What are phenolic disinfectants used for

Answer 33

General purpose environmental disinfectants

Question 34

When are peroxygenated compound disinfectants used

Answer 34

For surface disinfection - good anti-microbial properties

Question 35

What kinds of surface active agents are there

Answer 35

Anionic, cationic, non ionic, Amphoteric detergents

Question 36

Are gram positive or negative bacteria generally more sensitive to disinfectants

Answer 36

Gram positive are more sensitive

Question 37

What spore producing microbes are highly resistant to disinfectants

Answer 37

Bacterial spores - highly resistant

Question 38

What type of viruses are quite sensitive to disinfectants

Answer 38

Enveloped or lipophilic viruses (HIV)

Question 39

What type of viruses are not very susceptible to disinfectants

Answer 39

Hydrophilic (Polioviruses and other enteroviruses)

Question 40

When should and instrument be sterilised

Answer 40

Any instrument that comes routinely into contact with blood, saliva or tissue that are surgically breached should be sterilised, any other should be disinfected

Question 41

What in the GD practice is disinfection generally used for

Answer 41

- Decontamination of surfaces - Treatment of spillages - Decontamination of areas known to be grossly contaminated - Decontamination of non-surgical instruments - Decontamination prior to sterilisaiton - Decontamination of dental unit water supplies

Question 42

What are the 3 main sources of infection in the GD practice

Answer 42

- Patients suffering from the infectious disease - Patient in the prodromal stage of certain infections - Individuals who are carriers of pathogenic micro-orgnaisms

Question 43

What are the 3 main ways of infection transmission in the GD practice

Answer 43

- Direct contact of tissues with skin or body fluids - By droplets containing infectious agents - Via contaminated instruments that haven't been rendered safe for re-use

Question 44

What are the advantages and disadvantages of using the Autoclave for sterilisation

Answer 44

Advantage: Running costs low Disadvantages: Apparatus is expensive and it rusts the dental instruments

Question 45

How do Chemiclaves work

Answer 45

Various micro-biocidal substances at high temps usually in vapour form

Question 46

What are some advantages and disadvantages for using the chemiclave for sterilisation

Answer 46

Advantages: Does not rust dental instruments; cycles cannot be interrupted Disadvantages: Long cycle time; vapours may be harmful; Machine needs careful maintenance; Chemicals involved are expensive

Question 47

What are the advantages and disadvantages of hot air ovens

Answer 47

Advantages: Very cheap to run Disadvantages: long cycle; not reliable even when fitted with circulatory fans; Damages instruments; sterilisation cycles can be interrupted