M18 - Disinfection and sterilization

Question 1

what is the definition of disinfection?

Answer 1

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

Question 2

what is an antiseptic?

Answer 2

antimicrobial agent that can be applied safely to the surface of the body or exposed tissues

Question 3

Describe the cleaning involved in disinfection.

Answer 3

– Reduce the bioburden (organic material, living & dead)
– Manual or automated
– Hot water & detergent, rinse thoroughly & dry
- improve success of downstream disinfection and sterilisation
(removing anything that complicates the disinfection process)

Question 4

Describe the heat involved in disinfection.

Answer 4

– a) Pasteurisation 63 ̊C 30 mins or 72 ̊C for 20 minutes
– b) Boiling Water 10 mins
– c) Washing & Rinsing 70 ̊C to 90 ̊C

(using heat to disrupt molecules)

Question 5

Describe the ultrasound involved in disinfection.

Answer 5

– a) high frequency sound waves
– b) remove dirt also disrupt cells, membranes.
– c) used in preparation of material prior to autoclaving

Question 6

Describe the chemicals involved in disinfection.

Answer 6

– Disinfectants - for inanimate objects

– Antiseptics - for living tissue

Question 7

Describe the action of alcohol’s in reducing microbes on skin and mucous membranes.

Answer 7

– Not pure i.e. 70%
– Requires wet contact for 3 minutes
– Kill bacteria rapidly (30 secs on dry surface)
– Inactive against spores & some fungi, expensive
– Evaporates, flammable & inactivated by organic material
– Skin antiseptic before injection

Question 8

Describe the action of cetrimide (savlon) in reducing microbes on skin and mucous membranes.

Answer 8

– Low level disinfectant
– Quaternary ammonium compounds
– cationic surface active detergents
– denature membranes
– effective cleansing agent
– inactivated by many substances including anionic detergents, soap and water
( i.e disruption of bacterial membranes using charged molecules )

Question 9

Describe the action of Chlorhexidine in reducing microbes on skin and mucous membranes.

Answer 9

– Non toxic to skin and mucous membranes
– Inactivates Staphylococci,not so active against other bacteria
– Readily inactivated
– Mouthwash (problem;taste and toothstaining)
– Hibitane skin disinfectant
– Hibiscrub hand disinfectant
-Hibisol rapid drying hand disinfectant (alcohol&detergent)

Question 10

Describe the action of Iodine in reducing microbes on skin and mucous membranes.

Answer 10

– Betadine (surgical scrub e.g. hebiscrub allergy)
– Very active against wide spectrum of bacteria
– Some activity against spores, fungi & viruses
– Inactivated by organic material
– Can cause skin reaction & stain skin
– Iodophors (combination of iodine & detergent)
– 2.5% Iodine in water or alcohol, 2 mins, excellent skin antiseptic

Question 11

Describe hypochlorites action in reducing microbes on inanimate objects.

Answer 11

– Strong hypochlorite 1% solution;
• for impression disinfection with visible blood contamination
expose for 2 mins
• spills of vomit, sputum, blood, leave for 10-20mins & wash with detergent.
– Weak hypochlorite 0.1% solution
• for impression disinfection with no blood contamination expose
for 10 mins
• General environment disinfectant (e.g. floors, walls, toilets)

Question 12

Describe phenols action in reducing microbes on inanimate objects.

Answer 12

• Denature proteins and disrupt cell membranes
• Hycolin 1%
• Used for spills of difficult materials e.g faeces
• Can be used with detergents without loss of activity

Question 13

Describe alcohols action in reducing microbes on inanimate objects.

Answer 13

– Surface cleaner, dental chair, work surface
– Bactericidal, vegetative bacteria, TB, fungi & viruses
– Do not inactivate spores
– Denaturation of protein & membrane disruption
– Evaporates; so short term disinfection

Question 14

what is considered when using disinfectants?

Answer 14

•  Is disinfection required?
–What level/type of contamination ,future use of material
•  Spectrum
–  Range of antimicrobial activity
•  Rate of action
–  Length of exposure
–  Number of Organisms (type) –  Temperature
–  Dilution/Volume
–  Presence of Organic matter
•  Type of action 
–  Bacteriocidal
–  Bacteriostatic
•  Effect of pH.
–  Phenols must be at the correct pH for activity 
•  Stability
–  should be made fresh
–  used material discarded
•  Contact time

Question 15

What is the definition of sterilisation?

Answer 15

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

Question 16

what is the medical definition of sterilisation?

Answer 16

one in a million instruments has one bacteria

Question 17

what are the methods of sterilisation?

Answer 17

• Heat (autoclave)
• Chemical
• Radiation (gamma -irradiation)
• Filtration

Question 18

what is considered when choosing the type of sterilisation?

Answer 18

–  Purpose
–  Nature of material
–  Nature of
Contamination
–  Convenience (time)

Question 19

In pattern of microbial death , what is the D Value?

Answer 19

– decimal reduction time

“time taken to reduce the viable number of organisms by 90%”

Question 20

what is the bioburden?

Answer 20

number of bacteria present

Question 21

what is the nature of sterilisation media?

Answer 21

proteinaceous organic material increase chance of survival

Question 22

Describe sterilisation by DIRECT heat.

Answer 22

– Heating metal object to white hot
– Flaming a metal loop or forceps in bunsen
– Incineration of combustible waste

Question 23

Describe sterilisation by DRY heat.

Answer 23

– Kills by destructive oxidation of essential cell constituents.
– Hot air oven
– Article placed in container
– Efficiency linked to temperature & time
– 160 ̊C for 120 mins, 180 ̊C for 30 mins
– e.g. metal instruments, mirrors, burs, files, reamers, glassware

Question 24

Describe sterilisation by MOIST heat.

Answer 24

Kills by coagulating & denaturing enzymes & structural
proteins
– Steam, steamer or boiling water bath 100 ̊C for 30mins – Autoclaving (quick & reliable)
• Principle at higher temperatures than >100 ̊C water boils
• Closed vessel, steam pressure rises, temperature rises.
• Higher pressure, higher temperature & shorter time.

Question 25

How does an autoclave work?

Answer 25

kills by coagulating and denaturing enzymes and structural proteins

Question 26

what are in the conditions in an autoclave?

Answer 26

(2.25 bar) 134 ̊C for 3 mins

Question 27

what is the 3 minutes referring to?

Answer 27

Holding time

Question 28

what are the controls for heat sterilisation?

Answer 28

• Record sheet & probe
• Browne s tubes chemical changes red to green.
• Autoclave tape & Chemical Indicator strips
• Spore strips (biological method)

Question 29

Describe sterilisation by chemicals.

Answer 29

• Formaldehyde Vapour
– Used in fumigation of cabinets/buildings etc
• 2% Gluteraldehyde
– buffered to alkaline pH
– inactivated by organic material
– Cidex sensitises skin (wear gloves)
– Procedure; wash in hot water & detergent, immerse in fresh
2% Glut solution, leave for 12h, rinse in sterile water, store under sterile conditions.

(not getting asked questions on it?)

Question 30

what are the two types of sterilisation by radiation?

Answer 30

• ultraviolet

- ionizing

Question 31

Describe ionising radiation.

Answer 31

– High energy, good penetration
– Carcinogenic g radiation generated from sealed/ shielded source
– Cobalt 60 source for cold sterilisation
– Large scale sterilisation of disposables, needles, syringes, chemicals.

Question 32

Describe sterilisation by filtration.

Answer 32

• Filter removes microorganisms
– Mechanical process, size exclusion
– Ideal for solutions or gases
– Filter cellulose nitrate or acetate of known pore size
– 0.2 mms remove most bacteria but not viruses
– High Efficiency Particulate Air filters 0.3 mms