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y3 medicine > sterilisation > Flashcards

sterilisation Flashcards

1
Q

What are the 2 general approaches to producing sterile products?

A
  1. produce under ‘clean’ conditions then terminally sterilise at the end
  2. make under completely sterile conditions (Aseptic processing)
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2
Q

where do microbial contaminants come from?

A 
raw materials (natural and synthetic)
water
manufacturing environment (people, equipment)
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3
Q

what is the difference between resident and transient microorganisms?

A

resident: soil, water, animals, human, plants - always present
transient: MO carried by vectors such as air and water. -move around so harder to control

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4
Q

define sterile and sterilisation:

A

sterile: free of all viable microorganisms
sterilisation: removal/killing of all viable microorganisms

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5
Q

how is an antibiotic solution sterilised?

A

liquid: by filtration
vial: moist heat sterilisation
stopper: EtO sterilisation

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6
Q

who regulates sterilisation processes?

A

EN and FDA

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7
Q

what do sterilisation standards aim to do?

A
  • control number of MOs in manufacturing environment
  • validate sterilising agent
  • validate sterilisation process
  • monitor sterilisation process
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8
Q

why is the kill curve asymptote?

A

as its logarithmic so never reaches 0 - has an infinite probability of survival

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9
Q

if you plot log of survivors against time, what can be calculated by the gradient?

A

thermal death rate

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10
Q

define D value:

A

the time taken at a fixed temp/conc of sterilant to reduce population by 90%

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11
Q

define Z value:

A

the temp change required to have a 90% reduction in D value (only applies to HEAT sterilisation)

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12
Q

what is Z value a measure of?

A

thermal resistance and a measure of efficiency

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13
Q

what is the reference organism for D value?

A

bacillus sterothermophilus - moist heat 10degrees

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14
Q

what is the reference organism for Z value?

A

bacillus subtilise - dry heat 20degrees

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15
Q

what is the SAL level?

A

10 to the -6

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16
Q

in words, how do you calculate whats needed to reach SAL?

A

on graph, take the starting number of MO and extrapolate down to 10 to the -6
calculate the reduction level
say reduction is x, then times this by the D value
this value is how long the product needs to be exposed for in order to reach SAL

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17
Q

what is D value influenced by?

A 
bacterial species
vegetative or spore forming 
production method
nutrient environment 
treatment dose
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18
Q

why is bioburden estimation important?

A

in order to specify sterilisation parameters and inactivation kinetics

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19
Q

what are the steps involved in bioburden estimation? (8 steps)

A
  1. selection
  2. collection
  3. transfer to lab
  4. treatment if required (indirect)
  5. transfer to culture medium
  6. incubation
  7. enumeration
  8. data interpretation
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20
Q

whats the difference between direct and indirect methods of bioburden estimation?

A

direct: direct contact with culture medium
indirect: contact with eluent –> physical treatment –> transfer to culture medium

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21
Q

what factors does choice of culture medium depend on? (for bioburden estimation)

A

number of colony forming units
number of colony types
(the more of both, the better)

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22
Q

define process validation:

A

the establishment of documentary evidence that provides a high degree of assurance that a specific process will consistently produce a product its pre-determined specifications (SAL of 10 to the -6)

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23
Q

what is process validation divided into?

A

installation qualification and performance qualification

performance qualification is split into physical (better) and microbiological qualification

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24
Q

define biological indictors:

A

an inoculated carrier contained within its primary pack ready for use and providing a defined resistance to the specified sterilisation process
they provide a means of assessing directly the microbial lethality of a sterilisation process

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25
Q

what are biological indicators characterised by? (9 things)

A
  • strain of test organism
  • reference to culture collection
  • manufacturers name
  • number CFUs per test piece
  • D value
  • Z value
  • recommended storage conditions
  • expiry date
  • disposal instructions
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26
Q

choice of BI depends on…

A

stability
resistance
non-pathogenic (to workers)
recoverability (those that survive should be able to be recovered on an agar plate)

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27
Q

recorded BI for validation of filtration sterilisation?

A

brevundimonas diminuta

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28
Q

how do you select which sterilisation process to use?

A

variables should be controlled and monitored throughout
not hazardous to workers or environment
doesn’t leave toxic residues within the product

29
Q

define filtration:

A

passage of a fluid (liquid of gas) across a filter, removing any contaminating solutes

30
Q

what are the 4 ways in which bacteria smaller than the filter are still not filtered out?

A
  • irregular shape
  • simultaneous arrival
  • blocked pore
  • surface interactions (-ve bacteria and +ve filter)
31
Q

what is filter voidage?

A

empty space within a filter where the bacteria can accumulate so even though bacteria may pass the pore, it will remain in the voidage so filter voidage is good

32
Q

what are the 2 filter types?

A

depth and screen (both usually used together)

33
Q

characteristics of depth filter:

A 
variable pore size
relies on inertial impaction
high retentive capacity 
cheap
robust
doesn't produce sterile product
34
Q

characteristics of screen filter:

A 
uniform pore size
direct interception 
easily blocked
fragile
expensive 
produces sterile product
35
Q

how do you validate the filtration sterilisation process?

A
  1. physical: bubble point pressure test - used to test correct pore size
  2. use the recommended BI (brevundimonas diminuta) where minimum removal should be 10^7/cm2 but manufacturers aim for 10^10/cm2
36
Q

how do bacteria die by moist heat sterilisation?

A

protein coagulation and hydrolysis

37
Q

how do bacteria die by dry heat sterilisation?

A

oxidative processes

38
Q

what is moist heat sterilisation used to sterilise?

A

aqueous products, devices and dressings

39
Q

what is dry heat sterilisation used to sterilise?

A

dry products, oil preps, glassware and instruments

40
Q

what equipment is used for dry heat sterilisation compared to moist heat sterilisation?

A

dry:
dry heat oven
sterilising tunnel

moist:
autoclave

41
Q

what are the mechanisms of heat transfer for dry heat compared to moist heat sterilisation

A

dry: conduction, radiation and convection
moist: latent heat of vaporisation (downward displacement of steam)

42
Q

what are the critical aspects of dry heat sterilisation?

A

product size
loading pattern
air circulation

43
Q

what are the critical aspects of moist heat sterilisation?

A

air removal
saturated stem
steam under pressure

44
Q

what are the steps involved in a dry heat cycle?

A

drying
heating
exposure
cooling

45
Q

what are the steps involved in a FLUID moist heat cycle?

A 
air removal
heating
sterilisation
cooling 
drying
46
Q

what are the 3 different autoclave cycle types?

A

fluid
porous load
air ballasted

47
Q

how do you validate moist sterilisation process?

A

MTR - 12 thermocouples in chamber (specific to 1 load only)
or
TRC - 1 probe in drain of autoclave

48
Q

what is the Fo concept? in my words

A

because compendia cycles are go too far into sterile level (way passed 10^-6) so this leads to gross overkill and product degradation
Fo is used to tell you how long (minutes) a product needs to be exposed for in order to be sterile

49
Q

what is the minimum Fo value?

A

8 mins (not just holding time but the length of time of whole process)

50
Q

what is the main advantage using Fo compared to using compendial cycles?

A

Fo allows lethalities to be compared and can be used to heat labile products

51
Q

define Fo:

A

the lethality expressed in terms of the equivalent time in mins at a temp of 121degrees delivered by the process to the product in its final container with reference to microorganisms possessing a Z value of 10

52
Q

using biological data, what is the equation used to calc Fo?

A

Fo = D (logNo - logN)

53
Q

using thermal data, what is the equation used to calc Fo?

A

Fo = [log-1 (T-121/Z)] x dt

54
Q

how is Fh different to Fo?

A

Fo is only for moist heat sterilisation
Fh is for dry heat sterilisation
Fh Z value is 20 whereas Fo is 10
reference temp for Fh is 170 whereas Fo is 121

55
Q

what are the advantages of radiation sterilisation?

A 
can be used for heat labile products
safe
reliable
continuous/batch process
reproducible 
easy process
56
Q

what is radiation sterilisation used to sterile?

A 
single use medical devices
surgical devices
containers
wrapping materials 
powders in bulk
CAN ONLY STERILISE DRY PRODUCTS
57
Q

how does radiation sterilisation work?

A
  • exposure to high energy radiation so that the energy released is enough to eject an electron from the atom
  • inactivates MOs
  • chemical change of bacteria breaks their bonds and kills them
58
Q

how can you measure the absorbed dose of radiation?

A

using a dosimeter

59
Q

what is the usual ionisation source for radiation sterilisation?

A

cobalt (60Co)

60
Q

what is the minimum dose of radiation used?

A

25kGy

61
Q

how does chemical sterilisation work?

A

EtO is an alkylating agent that disrupts the DNA of MO so they can’t reproduce

62
Q

what is chemical sterilisation used to sterilise?

A

medical devices and display items

63
Q

what is chemical sterilisation affected by?

A

temp (25-65 degrees)
time (1-24hrs)
humidity (40-85%)
conc of EtO (250-1200mg/L)

64
Q

what is the recommended BI for chemical sterilisation?

A

bacillus subtilus

65
Q

what are the major concerns with chemical sterilisation?

A

toxicity to workers

produces carcinogenic substances

66
Q

what are the stages in the process of chemical sterilisation?

A
  1. pre-conditioning (allow to drop to right humidity)
  2. sterilisation (7 steps to it)
  3. aeration room (exposed to sterile air to remove residues)
67
Q

what are the 7 steps involved in the sterilisation part of chemical sterilisation?

A
  • evacuation (removal of all air)
  • vacuum hold
  • conditioning (product is heated at subatmospheric pressure)
  • sterilant injection – stage at which EtO is inputted
  • exposure sterilant removal
  • flushing
68
Q

what are the new sterilisation technologies?

A
  • x-ray irradiation (expensive and low power)
  • pulsed light (broad spectrum white light)
  • microwaves (intense heating, used for contact lenses)
  • gas plasma (mixture of ions, free rads, electrons and neutrons)

y3 medicine (8 decks)

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