sterilisation Flashcards
What are the 2 general approaches to producing sterile products?
- produce under ‘clean’ conditions then terminally sterilise at the end
- make under completely sterile conditions (Aseptic processing)
where do microbial contaminants come from?
raw materials (natural and synthetic) water manufacturing environment (people, equipment)
what is the difference between resident and transient microorganisms?
resident: soil, water, animals, human, plants - always present
transient: MO carried by vectors such as air and water. -move around so harder to control
define sterile and sterilisation:
sterile: free of all viable microorganisms
sterilisation: removal/killing of all viable microorganisms
how is an antibiotic solution sterilised?
liquid: by filtration
vial: moist heat sterilisation
stopper: EtO sterilisation
who regulates sterilisation processes?
EN and FDA
what do sterilisation standards aim to do?
- control number of MOs in manufacturing environment
- validate sterilising agent
- validate sterilisation process
- monitor sterilisation process
why is the kill curve asymptote?
as its logarithmic so never reaches 0 - has an infinite probability of survival
if you plot log of survivors against time, what can be calculated by the gradient?
thermal death rate
define D value:
the time taken at a fixed temp/conc of sterilant to reduce population by 90%
define Z value:
the temp change required to have a 90% reduction in D value (only applies to HEAT sterilisation)
what is Z value a measure of?
thermal resistance and a measure of efficiency
what is the reference organism for D value?
bacillus sterothermophilus - moist heat 10degrees
what is the reference organism for Z value?
bacillus subtilise - dry heat 20degrees
what is the SAL level?
10 to the -6
in words, how do you calculate whats needed to reach SAL?
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
what is D value influenced by?
bacterial species vegetative or spore forming production method nutrient environment treatment dose
why is bioburden estimation important?
in order to specify sterilisation parameters and inactivation kinetics
what are the steps involved in bioburden estimation? (8 steps)
- selection
- collection
- transfer to lab
- treatment if required (indirect)
- transfer to culture medium
- incubation
- enumeration
- data interpretation
whats the difference between direct and indirect methods of bioburden estimation?
direct: direct contact with culture medium
indirect: contact with eluent –> physical treatment –> transfer to culture medium
what factors does choice of culture medium depend on? (for bioburden estimation)
number of colony forming units
number of colony types
(the more of both, the better)
define process validation:
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)
what is process validation divided into?
installation qualification and performance qualification
performance qualification is split into physical (better) and microbiological qualification
define biological indictors:
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
what are biological indicators characterised by? (9 things)
- 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
choice of BI depends on…
stability
resistance
non-pathogenic (to workers)
recoverability (those that survive should be able to be recovered on an agar plate)
recorded BI for validation of filtration sterilisation?
brevundimonas diminuta
how do you select which sterilisation process to use?
variables should be controlled and monitored throughout
not hazardous to workers or environment
doesn’t leave toxic residues within the product
define filtration:
passage of a fluid (liquid of gas) across a filter, removing any contaminating solutes
what are the 4 ways in which bacteria smaller than the filter are still not filtered out?
- irregular shape
- simultaneous arrival
- blocked pore
- surface interactions (-ve bacteria and +ve filter)
what is filter voidage?
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
what are the 2 filter types?
depth and screen (both usually used together)
characteristics of depth filter:
variable pore size relies on inertial impaction high retentive capacity cheap robust doesn't produce sterile product
characteristics of screen filter:
uniform pore size direct interception easily blocked fragile expensive produces sterile product
how do you validate the filtration sterilisation process?
- physical: bubble point pressure test - used to test correct pore size
- use the recommended BI (brevundimonas diminuta) where minimum removal should be 10^7/cm2 but manufacturers aim for 10^10/cm2
how do bacteria die by moist heat sterilisation?
protein coagulation and hydrolysis
how do bacteria die by dry heat sterilisation?
oxidative processes
what is moist heat sterilisation used to sterilise?
aqueous products, devices and dressings
what is dry heat sterilisation used to sterilise?
dry products, oil preps, glassware and instruments
what equipment is used for dry heat sterilisation compared to moist heat sterilisation?
dry:
dry heat oven
sterilising tunnel
moist:
autoclave
what are the mechanisms of heat transfer for dry heat compared to moist heat sterilisation
dry: conduction, radiation and convection
moist: latent heat of vaporisation (downward displacement of steam)
what are the critical aspects of dry heat sterilisation?
product size
loading pattern
air circulation
what are the critical aspects of moist heat sterilisation?
air removal
saturated stem
steam under pressure
what are the steps involved in a dry heat cycle?
drying
heating
exposure
cooling
what are the steps involved in a FLUID moist heat cycle?
air removal heating sterilisation cooling drying
what are the 3 different autoclave cycle types?
fluid
porous load
air ballasted
how do you validate moist sterilisation process?
MTR - 12 thermocouples in chamber (specific to 1 load only)
or
TRC - 1 probe in drain of autoclave
what is the Fo concept? in my words
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
what is the minimum Fo value?
8 mins (not just holding time but the length of time of whole process)
what is the main advantage using Fo compared to using compendial cycles?
Fo allows lethalities to be compared and can be used to heat labile products
define Fo:
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
using biological data, what is the equation used to calc Fo?
Fo = D (logNo - logN)
using thermal data, what is the equation used to calc Fo?
Fo = [log-1 (T-121/Z)] x dt
how is Fh different to Fo?
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
what are the advantages of radiation sterilisation?
can be used for heat labile products safe reliable continuous/batch process reproducible easy process
what is radiation sterilisation used to sterile?
single use medical devices surgical devices containers wrapping materials powders in bulk CAN ONLY STERILISE DRY PRODUCTS
how does radiation sterilisation work?
- 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
how can you measure the absorbed dose of radiation?
using a dosimeter
what is the usual ionisation source for radiation sterilisation?
cobalt (60Co)
what is the minimum dose of radiation used?
25kGy
how does chemical sterilisation work?
EtO is an alkylating agent that disrupts the DNA of MO so they can’t reproduce
what is chemical sterilisation used to sterilise?
medical devices and display items
what is chemical sterilisation affected by?
temp (25-65 degrees)
time (1-24hrs)
humidity (40-85%)
conc of EtO (250-1200mg/L)
what is the recommended BI for chemical sterilisation?
bacillus subtilus
what are the major concerns with chemical sterilisation?
toxicity to workers
produces carcinogenic substances
what are the stages in the process of chemical sterilisation?
- pre-conditioning (allow to drop to right humidity)
- sterilisation (7 steps to it)
- aeration room (exposed to sterile air to remove residues)
what are the 7 steps involved in the sterilisation part of chemical sterilisation?
- 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
what are the new sterilisation technologies?
- 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)
