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The Medicine - Y3 > Sterilisation > Flashcards

Sterilisation Flashcards

1
Q

What are the two approaches to achieving a sterile product?

A

1) Produce under ‘clean’ conditions and terminally sterilise in final container
2) Aseptic technique - produce under conditions free of microorganisms

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2
Q

What are the potential sources of microbial contamination within a manufacturing environment?

A

Raw material - synthetic and natural
Water - essential for microbial growth so if used to wash/cool products will increase growth
Manufacturing environment - air/equipment/personnel

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3
Q

What are the sources of resident microorganisms?

A

Water
Soil
Plants
Animals and humans

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4
Q

What are the sources of transient microorganisms?

A

Water and air is a vector for these microorganisms and they are harder to control

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5
Q

What is the definition of sterile?

A

Free of viable microorganisms

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6
Q

What is the definition of sterilisation?

A

The killing or removal of viable microorganisms

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7
Q

What are the sterilisation techniques that kill microorganisms?

A

Heat - dry/moist
Chemical - ethylene oxide
Radiation

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8
Q

What is the sterilisation process that removes microorganisms?

A

Filtration sterilisation

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9
Q

How would an antibiotic contained in a vial with a stopper be sterilised?

A

Antibiotic sterilised using filtration technique
Vial - Steam sterilisation as can’t pass through filter
Stopper - EtO
Antibiotic then filled in vial aspetically and sealed aseptically before it is packaged

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10
Q

What are sterilisation standards used for?

A

Control number of microorganisms
Validate the sterilising agent
Validate the sterilisation process
Monitor the sterilisation process

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11
Q

What is meant by an asymptote curve?

A

Each time it decreases by the same proportion but never reaches zero

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12
Q

What order of kinetics is demonstrated by inactivation kinetics kill curve?

A

First order

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13
Q

How is a kill curve produced?

A

Culture of cells taken and exposed to sterilant for increasing number of time
At different time points, remove a sample and perform a viable count
Plot the number of survivors against time to produce an asymptote curve

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14
Q

How can a kill curve be plotted to allow the calculation of a thermal death rate i.e. y and x axis?

A

Plot log of number of survivors against time to give a semi-logarithmic graph
Will give you a straight line so you can calculate the gradient and this is the thermal death rate (thermal if temp used)

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15
Q

An asymptote curve can be used to compare results when organism exposed to different temps and when different organisms exposed to the same temp. True or false?

A

False - use a semi-logarithmic graph for this

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16
Q

What are the four key points about inactivation kinetics?

A

Infinite probability of survival
First order kinetics
Organism specific
Affected by concentration of sterilant

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17
Q

Define D value

A

The time taken (at fixed temp/conc/radiation) to reduce the population of microorganisms by 90%

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18
Q

A 90% reduction in population of microorganisms is how many log cycles?

A

1

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19
Q

What are the units of D expressed as?

A

minutes

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20
Q

Z value is only for which type of sterilisation?

A

Heat sterilisation

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21
Q

Define Z value and interpret its meaning

A

The temp change required to reduce D-value by 90% i.e. temp change required to reduce the time taken to reduce pop by 90% by 90%

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22
Q

What are the units of Z-value?

A

Degrees C

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23
Q

How can thermal resistance be measured?

A

Z value

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24
Q

What can be used to make sense of data produced by Z-value?

A

Biological indicator used as a standard

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25
Q

Which BI is used in moist heat sterilisation?

A

Bacillus stearothermophilus - Z =10

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26
Q

Which BI is used for dry heat sterilisation?

A

Bacillus subtilus - Z = 20

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27
Q

What is used as an indicator of sterility?

A

SAL = 10-6

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28
Q

What is the length of your sterilisation process determined by?

A

Resistance of microorganism
Type of microorganism
Number of microorganisms present

29
Q

What are the 5 things that influence D-value?

A 
Bacterial species
Vegetative vs spore
Treatment dose
Production method
Nutrient environment
30
Q

What is the definition of bioburden estimation and what is its importance?

A

The population of viable microorganisms in or on a product/package
Important in specifying sterilisation parameters and inactivation kinetics

31
Q

What are the steps in bioburden estimation?

A 
Sample selection
Collect items for test
Transfer to test lab
Treat (if required)
Transfer to culture medium
Incubation
Eumeration and characterisation
Interpretation of data
32
Q

During the bioburden estimation process, the sample may need to be treated by removal of cells. What determines the technique used for removal?

A 
Ability to remove microbial contaminants
The effect of removal on viability 
Types and location of microorganisms
Nature of product
Culture conditions
33
Q

What are the different stages of process validation?

A

Installation qualification - checking steriliser works
Performance - checking it sterilises
Physical - checking levels of radiation/heat etc
Microbiological - confirms physical and for EtO as physical not poss

34
Q

What is a biological indicator and what is its use?

A

An innoculated carrier in a primary pack that provides definite resistance to a specified sterilisation process
It is used as a direct assessment of microbial lethality of a sterilisation process

35
Q

Which BI is used for filtration sterilisation?

A

Brevundimonas deminuta

36
Q

Which BI is used for radiation sterilisation?

A

Bacillus pumilus

37
Q

Which BI is used for EtO?

A

Bacillus subtilus

38
Q

What are BIs characterised by?

A 
D value 
Z value
CFU per test piece
Expiry date
Recommended storage conditions
39
Q

What 4 factors govern choice of BI?

A

Non-pathogenic
Recoverability
Resistance
Stability

40
Q

What is the specific guidance given for the selection of a sterilisation technique?

A

Agent needs to be in contact with all parts of the product
No toxicity
Not harmful/hazardous to operators of environment
Process variables are controlled and monitored

41
Q

Explain filtration sterilisation

A

Fluid passes across a filter removing any contaminating particles.
Particles that don’t pass:
- irregular shape
- simultaneous arrival of two particles
- large particle blocking the pore
- interaction between the particle and matrix of filter

42
Q

What are the two types of filters for sterilisation and outline key differences between them

A

Depth and screen
Depth filters have a non-uniform pore size, they have high voidage. They are cheap and robust and they don’t achieve sterility. Particles sediment by inertial impaction
Screen filters have uniform particle sizes, the pores are easily blocked. They are fragile and expensive but achieve sterility when the pore size is less than 0.22um. Particles sediment by direct interception

43
Q

What are the two methods of filter validation?

A

Bubble point pressure test - filter with water on top and apply pressure from bottom until bubbles form
Challenge filter with BI - brevundimonas diminuta and aim to achieve removal of 10^7 cells/cm^2

44
Q

How are microorganisms killed by moist heat sterilisation?

A

Hydrolysis and protein coagulation

45
Q

How are microorganisms killed by dry heat sterilisation?

A

Oxidative processes

46
Q

What technology is used for dry heat sterilisation and what are the mechanisms of heat transfer?

A

Technology: dry heat ovens and sterilising tunnels

Heat transfer: convection (most common), radiation, conduction

47
Q

What are the critical aspects of dry heat sterilisation?

A

Air circulation, loading pattern and particle size

48
Q

What are the 4 stages of a dry heat cycle?

A

Drying
Heating
Exposure
Cooling

49
Q

Why is moist heat sterilisation faster than dry heat sterilisation and which one is used more commonly?

A

Moist heat is faster as microorganisms are killed faster by oxidative processes than hydrolysis. Moist heat is more common

50
Q

What technology is used in moist heat sterilisation and what is the mechanism of heat transfer?

A

Autoclave

Latent heat of vaporisation

51
Q

What are the critical aspects of moist heat sterilisation?

A

Saturated steam
Air removal
Steam under pressure

52
Q

What are the critical lethal parameters of moist heat sterilisation?

A

Dry saturated steam not wet
Temperature +/- 5K of limit
Time of contact - sufficient to give SAL 10^-6
Bioburden level

53
Q

What are the 5 stages of autoclave operation for moist heat sterilisation?

A 
Air removal
Heat
Sterilise
Cool
Dry
54
Q

What are the 3 autoclave cycle types for moist heat sterilisation?

A

Porous load - fabrics
Fluid cycle - glassware
Air ballasted cycle - plastic

55
Q

What are the validation methods used for moist heat sterilisation

A

Master temperature record - thermocouples - min 12

Temperature record chart - drain probe temp

56
Q

What is moist heat sterilisation used for?

A

Aqueous products
medical devices
dressings

57
Q

What is dry heat sterilisation used for?

A

Dry powders
Oil preparations
Glasswear

58
Q

What is radiation sterilisation used for?

A

Single use medical devices

Containers

59
Q

How does radiation sterilisation kill microorganisms?

A

Radiation induces chemical change in the vital components of the microbial cell by ejection of orbital electrons from the atom or molecule -> death

60
Q

What is the minimum sterilisation dose for radiation sterilisation?

A

25kGy

61
Q

What is the ionising source for radiation sterilisation?

A

Cobalt 60

62
Q

What is EtO sterilisation used for?

A

Disposable items

63
Q

How does EtO sterilisation work?

A

Alkylation of sulfhydryl, amino and carboxyl groups on proteins and nucleic acids

64
Q

All sterilisation methods provide the same levels of sterility. True or false?

A

False - EtO doesn’t provide same levels

65
Q

Which sterilisation method can leave toxic residues post sterilisation?

A

EtO

66
Q

What are the critical lethal parameters for EtO?

A 
Time - 1-24hrs
Temp - 25-65 degrees
Relative humidity - 40-85%
EtO concentration - 250-1200mg/L
BI: bacillus subtilus
67
Q

What equipment is used in EtO sterilisation?

A

Pre-conditioning
Sterilising
Aeration

68
Q

Name some new and emerging technologies for sterilisation and identify some of the problems they raise

A

X-ray
Microwaves
Pulsed light
They have unknown lethal effects and no established regulatory requirements

69
Q

What are the 7 steps in the EtO sterilisation cycle?

A 
Evacuation
Vacuum hold
Conditioning 
Sterilant injection
Exposure
Sterilant removal
Flushing

The Medicine - Y3 (3 decks)

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