Sterilisation Processing Flashcards
1
Q
What are the 2 approaches to making sterile products?
A
1) Produce under ‘clean conditions’ then terminally sterilise - ‘terminal sterilisation’
2) Produce and assemble under conditions ‘free of microorganisms’, essentially mixing sterile components together to give an active - ‘aseptic processing’
2
Q
What are some sources of microbial contaminants within the manufacturing environment?
A
Raw materials
Operators
Equipment and facilities
Water and air as vectors
3
Q
Why are raw materials more of a worry when considering microbial contaminants?
A
Natural materials have a greater range of microbes vs. synthetic or semi-synthetic materials
4
Q
M/o normally found in a particular environment are referred to as what?
A
Resident
5
Q
What happens when a contaminant is found in the manufacturing environment?
A
Identified by genus and species
Identification can indicate the source since different environments are characterised by different microbes
6
Q
What m/o are found in soil?
A
Endospore producing
Fungi
Mainly gram +ve
7
Q
What m/o are found in water?
A
Gram -ve (due to cell wall structure)
Yeasts and moulds
8
Q
What m/o are found in animals/humans?
A
Gram +ve/-ve
Obligate anaerobes
Dependent on touch transfer, personal hygeine, sneezing, coughing etc.
9
Q
What m/o are found in plants?
A
Yeasts and moulds
10
Q
What are transient organisms?
A
Those that are shed in one place and are carried by vectors (air, water, operators) to another site
11
Q
Define ‘sterile’
A
Free of viable microorganisms
An absolute term, something cannot be ‘quite’ sterile
12
Q
Define ‘sterilisation’
A
Killing or removal of all viable microorganisms
13
Q
What are the traditional methods of sterilisation processing?
A
Killing e.g. radiation, heat (moist/dry), chemical (EtO)
Complete removal e.g. filtration
14
Q
All sterilisation processes are governed by what?
A
A set of international standards for consistency e.g. EN, FA and Japanese
15
Q
Standards provide guidance on what?
A
Validating sterilising agent
Validating sterilisation process
Monitoring sterilisation process
Control of m/o in the manufacturing environment
16
Q
How is sterilisation assessed?
A
By measuring the rate and degree of kill of a microorganism
17
Q
How can a kill curve be calculated?
A
Using heat as the example
You would take an overnight culture, expose it to a specific temperature and remove a sample at regular intervals counting the no. of viable m/o’s present
18
Q
How can we count the no. of viable m/o’s present without knowing how many we’re starting off with?
A
Serial dilution
Only plates with a cfu count 30-300 are counted (less and its not statistically significant, more, and its too difficult to count as the microorganisms merge)
You know your serial dilution factor so you can simply use this to multiply up
19
Q
How can data from a kill curve experiment be represented?
A
Table
Graph preferred
20
Q
What are the axis on a kill curve graph?
A
No. of survivors on the y-axis
Time on the x-axis
21
Q
What can be said about the kill curve graph? (shape, usefulness)
A
Asymptote curve - for each unit of time you get a fixed proportion of cells being killed, but the curve will never reach zero (frog and lillypad)
Not as useful due to its shape (can’t calculate gradient)
22
Q
How can the kill curve graph be altered to help us make more sense of the data?
A
Semi-logarithmic version can be plotted
Gives a linear relationship allowing us to calculate gradient
23
Q
What does the gradient of a semi-logarithmic kill curve graph equal?
A
Thermal death rate - how quickly m/o dies at a particular temperature
24
Q
The higher the temperature an organism is exposed to (kill-curve graph)?
A
The steeper the gradient and the faster the rate of kill
Applies to examples other than temperature (EtO, radiation)
25
What are the 3 key points on inactivation kinetics?
1) Inactivation demonstrates 1st order kinetics (straight line)
2) There is an infinite probability of survival (asymptote curve)
3) Can be affected by sterilant dose and is organism specific
26
Define D-value
The time taken, at a fixed temperature, to reduce the population by 90% or 1-log cycle
27
What are 2 reasons D-values are useful?
Allow comparisons of resistance across different organisms
| Guide manufacturers on how long they should process a sample for
28
How is D-value calculated?
Plot of log survivors against time
Draw 2 lines, one log cycle apart
The time difference is your D-value
29
Define Z-value
The temperature change required to produce a 90% or 1-log cycle reduction in D-value
30
For which type of sterilisation is Z-value applicable?
Heat only
31
How is Z-value calculated?
Plot of log D value against temperature
32
Z-value can be described as a measure of what?
Thermal resistance
33
Z-value can be described as an indicator of what?
Efficacy
34
What needs to be done in order to make sense of Z-values?
Comparison to a reference set of standards
35
What is the standard BI for moist heat sterilisation?
| What is its Z-value?
Bacillus stearothermophillus endospores
| 10ᵒC
36
What is the standard BI for dry heat sterilisation?
| What is its Z-value?
Bacillus subtilus endospores
| 20ᵒC
37
What does a Z-value of 10ᵒC mean?
For every 10 degrees increase in temperature, there is a 90% reduction in D-value
38
Why are these standard BI's for Z-value comparison chosen?
Constant resistance
| Endospores are the most resistant form
39
What is the sterility assurance level? (definition)
Minimum value to which all sterilisation processes must adhere, but most aim beyond this
40
What is the sterility assurance level? (value)
10⁻⁶
| Could represent either one millionth of a microbial cell or more likely, 1 contaminated product in a batch of 1 million
41
Why do we need the sterility insurance level?
Sterile is defined as zero microbes being present yet on an inactivation curve there is no 0
42
Define 'bioburden'
A population of viable microorganisms on or in a product/package
43
If we know the initial bioburden, how can we calculate the time taken to achieve the sterility assurance level?
Example
Bioburden of 10²
SAL 10⁻⁶
D-value 2 mins
We need an 8-log cycle reduction and the D-value represents a 1-log cycle reduction
2minutes x 8 log cycles = 16 minutes to achieve SAL
44
Time to SAL is influenced by what 3 factors?
D-value
Initial bioburden
Time of heating
45
D-values are influenced by what 5 factors?
```
Vegetative/endospore
Bacterial species
Production method
Nutrient environment
Treatment dose
```
46
What are the 8 stages of bioburden estimation?
1) Sample selection
2) Collection of items for test
3) Transfer to test lab
4) Treatment (if required)
5) Transfer to culture medium
6) Incubation
7) Enumeration and characterisation
8) Interpretation of data
47
Which of the 8 stages of bioburden estimation represent the most variability?
Transfer to test lab, treatment, transfer to culture medium and incubation (3-6)
48
Removal techniques can adopt 2 generalised approaches, what are these?
Direct - product, contact with culture medium, incubation and enumeration
Indirect - product, contact with eluent, physical treatment, transfer to culture medium, incubation and enumeration
49
What are the 4 considerations needed when selecting a removal technique?
Ability to remove microbial contamination
Effect of removal method on microbial viability
Nature of product
Culture conditions
50
Define CFU
Colony forming units, total no. of cells
51
How can you decide which culture condition is best?
That with the highest CFU and greatest variety of organisms (highest no. of colony types)
52
What are the 3 stages of process operation?
1) Cycle development - lab studies, effect of your sterilant on m/o
2) Cycle validation - providing proof your process works
3) Cycle monitoring - ensures consistency of desired end result
53
What does process validation involve? (2)
Installation qualification
| Performance qualification
54
What does performance qualification involve? (2)
Physical quantification
| Microbiological qualification
55
What does physical quantification involve?
Preferred
Involves taking a physical measurement
E.g. for an autoclave, monitor the temperature
Consistent and not subject to change
56
What does microbiological quantification involve?
Back up to physical or where physical cannot be used (e.g. EtO sterilisation)
Involves using m/o's with a high and defined resistance
57
What is a downside to microbiological quantification?
Because they're biological, they are more prone to error and variability, changes in genotype etc.
58
Define 'biological indicator'
An inoculated carrier contained within its primary pack ready for use and providing a defined resistance to the specified sterilisation process
59
What is the purpose of biological indicators?
Provide a means of directly assessing microbial lethality of a sterilisation process
Idea is that if you can kill the most resistant organism, anything with a lesser resistance will be killed
60
When are BI's used?
Validation for steam, dry heat, radiation, EtO
| Monitoring of EtO sterilisation (no accurate physical method of monitoring EtO sterilisation)
61
How are BI's used in practice?
Proportion of test organisms surviving the process are measured and related to the expected lethality of the process
62
How are biological indicators characterised? (9)
```
Strain of test organism
Reference to culture collection
Manufacturer name
Number (10⁶) CFU's per piece/test strip
D-value (at different temperatures)
Z-value
Recommended storage conditions
Expiry date
Disposal instructions
```
63
What are the factors governing choice of BI? (4)
Stability - don't want it to fluctuate in terms of resistance
Resistance - high in comparison to bioburden, usually bioburden is vegetative cells so spores will be more resistant
Non-pathogenic - don't want them to pose a threat to the operator
Recoverability - if spores remain after treatment, you need to be able to recover these and grow them to figure out why the process isn't working
64
What is the recommended test BI for filtration?
Brevundimonas dimiuta
65
What is the recommended test BI for irradiation?
Bacillus pumilus
66
What is the recommended test BI for EtO?
Bacillus subtilus
67
What can be used to select sterilisation method?
EMEA decision tree
68
What is the default sterilisation method?
Heat
69
Which is preferred, terminal sterilisation or aseptic processing?
Terminal sterilisation
70
Define 'filtration'
Passage of fluid (liquid or gas) across a filter, removing any contaminating solutes
71
What are the 4 scenarios/problems that can occur during filtration?
Irregular shape
Simultaneous arrival
Blocked pore
Surface interactions
72
What is the filter voidage?
Open area within the filter
| Here where particles accumulate
73
What does it mean when you start to see accumulation on top of your filter?
Filter voidage is full
| Capacity has been reached
74
What are depth filters?
Non-fixed pore size
Rely primarily on inertial impaction
High retentive capacity
Cannot guarantee it will produce a sterile product
75
What are screen filters?
Uniform pore size (smaller, the more readily the filter will become blocked)
High flow rates and validated to minimum absorption
Direct interception
Easily blocked
Can produce a sterile product
76
What size pore size of a screen filter is needed to produce a sterile product?
0.22μm
77
Which is cheaper, depth or screen filters?
Depth
78
Which is more robust, depth or screen filters?
Depth
79
What 2 methods can be used to validate a filter?
Bubble point pressure test
| Challenge your filter with Brevundimonas dimiuta (0.4μm)
80
What is the minimum retainment requirement for a sterilising grade filter?
10⁷ cells/cm²
81
What is moist heat sterilisation?
Steam at temperatures >100ᵒC
82
How does moist heat sterilisation kill m/o's?
Death by protein coagulation and hydrolysis (fairly rapid death process)
83
For which products is moist heat sterilisation used?
Used for aqueous products, devices, dressings (must be heat stable)
84
Which is preferred by manufacturers, dry or moist heat sterilisation?
Moist heat
85
What is dry heat sterilisation?
Absence of moisture
86
How does dry heat sterilisation kill m/o's?
By oxidative processes (takes a lot longer vs. moist heat)
87
For which products is dry heat sterilisation used?
Dry powders, oil preparations, glassware and instruments
88
What equipment is needed for dry heat sterilisation?
```
Dry heat oven (like a domestic oven)
Sterilising tunnel (continuous processing)
```
89
What are the mechanisms of heat transfer present in dry heat sterilisation?
Conduction - from heating elements
Radiation - along the surface of shelves/walls
Convection - of the air within the chamber
90
What are the 3 critical aspects in dry heat sterilisation?
Product size - larger, longer to heat
Loading pattern - should allow for free circulation of air around the product
Air circulation - heats things more consistently, like a domestic 'fan-assisted' oven
91
What are the 4 stages of the dry heat cycle?
1) Drying
2) Heating
3) Exposure (holding period)
4) Cooling
92
What are pharmacopoeial cycles?
Combinations of temperatures and times (and pressure for moist heat) that guarantee a sterile product
93
What equipment is needed for moist heat sterilisation?
Autoclave (essentially a pressure cooker)
Stainless steel to resist pressure
Can be self-boiler (small scale) or use mains steam
94
What is the mechanism of heat transfer in moist heat sterilisation?
Latent heat of vaporisation
95
What are the 3 critical aspects in moist heat sterilisation?
Air removal - if there is any air present, unlikely to reach temperatures >100ᵒC needed to kill endospores, need to replace any air with steam
Saturated steam - can get different grades with different water contents
Steam generated under pressure
96
What type of steam is used in moist heat sterilisation?
Dry saturated
Not wet - too moist, could effect product quality
Not superheated - too dry, moves towards oxidative killing
97
What temperature should be used in moist heat sterilisation?
+/- 5 kelvin of limit
98
What are the 5 stages of an autoclave cycle?
1) Air removal
2) Heating
3) Sterilisation (holding period)
4) Cooling
5) Drying
99
What are the 3 different types of autoclave cycle?
1) Fluid cycle - most common, takes around 2 hours
2) Porous load - used for fabrics and dressings, takes around 30 minutes
3) Air ballasted cycle - very complex, varies by product
100
How can moist heat sterilisation be validated and monitored? (2)
Master Temperature Record (M.T.R)
| Temperature Record Chart (T.R.C)
101
What is the coolest part of the autoclave?
Drain, where cold air leaves
102
What is a problem with the reality of compendial/autoclave cycles?
Gross overkill
Problems of product degradation
Economically wasteful and expensive
103
What is compendial lethality?
Calculating the amount of lethality associated with the kill curve
104
What is Fo?
Alternative to compendial cycles
| Allows lethalities to be compared
105
Define 'Fo'
The lethality expressed in terms of the equivalent time in mins at a temperature of 121ᵒC delivered by the process to the product in its final container with reference to microorganisms possessing a Z-value of 10
106
What does Fo allow us to do?
Allows biological data to relate to thermal data e.g. calculate D-values, use these to determine Fo over a given time period, then use those Fo values to calculate a chosen time/temperature combo using thermal calculation
107
What are the 2 methods of calculating Fo?
1) Using biological data (cell count)
| 2) Using thermal data
108
What do both methods of calculation give us?
A measure of total process lethality
109
What is the minimum Fo?
8
| Equivalent to 8 mins at 121ᵒC
110
What are some of the benefits of using Fo values? (2)
Offer greater flexibility for heat sterilisation, can customise sterilisation cycles
Can be used for heat labile products to calculate the amount of time needed at a lower temperature for your product
111
What is the FH value?
Equivalent to Fo but for dry heat sterilisation (Fo is specific to moist heat sterilisation)
112
What is a problem with EtO sterilisation?
Currently no way of routinely monitoring EtO concentration
| Means it doesn't have the same level of sterility assurance as other methods
113
When is EtO stertilisation used?
For disposable, single-use items and 1/2 of all medical devices
114
How does EtO kill m/o's?
Causes alkylation of sulphahydryl, amino, hydroxyl and carboxyl groups of proteins and nucleic acids (blockage of reactive sites)
115
What is problematic about EtO's method of killing?
Target sites are not unique to bacteria meaning EtO can be quite toxic to humans also
116
Lethality of EtO sterilisation is affected by which 3 parameters?
Conc. of EtO
Temperature
Relative humidity
117
What must be included with the standard product load in EtO sterilisation?
A suitable BI
118
What are the safety concerns with EtO sterilisation?
Can leave toxic residues on the product
| High explosive
119
How are these safety concerns addressed?
Operator safety guidelines
| Mixed with CO₂ or N₂
120
What are the critical lethal parameters of EtO sterilisation?
Time - 1-24 hours
Temperature - 25-65ᵒC (helps to boost RH, varies depending on nature of product)
Humidity - 40-85% RH (EtO is more lethal in the presence of moisture)
EtO concentration - 250-1200mg/L
BI - B. subtilus
121
What are the 3 stages of the EtO process?
Pre-conditioning
Sterilisation
Aeration
122
What equipment is needed for EtO sterilisation?
In larger plants, you may have 3 distinct ares for each of these processes in a building
In smaller plants, a single steam chamber is used for all 3
123
What are the 7 stages of sterilisation in EtO sterilisation?
1) Evacuation
2) Vacuum hold
3) Conditioning
4) Sterilant injection
5) Exposure (holding period)
6) Sterilant removal
7) Flushing
124
What does sterilising agent characterisation involve/should include? (4)
Precise description of nature and quality of agent
Demonstration of microbicidal effectiveness
Material effects
Safety and the environment
125
Give some examples of new and emerging sterilisation technologies. (4)
X-ray irradiation
Pulsed light
Gas plasma
Microwaves
126
What are some of the issues with new technologies? (5)
```
Unknown lethal effects
Kill kinetics different to traditional processes
Validation compliance
Monitoring problems
No established regulatory requirements
```
127
What are QC and QA?
QC - detect bug, act, validate
| QA - prevent bug, plan, verify
128
What generic tests are used in QC and QA? (4)
Bioburden estimation
Test for sterility
Test of sterility
Test for pyrogens (LAL test)
129
What is the 'test of sterility'?
Performed on devices exposed to a fraction of the specified sterilisation process - part of process development
Purpose is to validate sterilisation process
Similar in process to bioburden estimation - direct immersion in medium and incubate vs. removal by eluent and transfer to medium
130
What is a false positive when performing a 'test of sterility'?
Saying product contains microorganisms when it doesn't
131
What should you do if you think you have a false positive?
Establish the frequency of occurence
Perform a simulated test of 'sterile' samples
If you then get growth, you know its down to the operator
132
What precautions can be taken to minimise the occurence of false positives? (9)
```
Use environmentally controlled area/room
Use aseptic techniques
Avoid introducing contamination
Decontaminate test surfaces
Sterilise test equipment and materials
Minimise manipulations
Monitor and control incubator environment
Minimise aerosol production
Train personnel
```
133
What is a false negative when performing a 'test of sterility'?
Saying product is sterile when its not
134
What causes false negatives?
Inadequate culture conditions
Presence of microbiostatic/cidal substances
Large interval between treatment and testing
135
What is the 'test for sterility'?
Testing for a negative i.e. absence of m/o's
| Done at the end of the sterilisation process
136
The probability of rejecting a batch with a 'test for sterility' is a function of what?
Probability of rejection = 1 - (1-p)ⁿ
Where,
p= proportion contaminated
n= no. of items tested
137
Is the 'test for sterility' destructive?
Yes
138
What is the correct conclusion to be drawn from a 'test for sterility'?
The batch passes the test for sterility, not that the batch is sterile
The greater the no. of samples tested, the greater the probability of rejection
Imprecise method
139
What happens if a batch fails the 'test for sterility'?
Up to 2 further re-tests allowed
Reject on 2nd if same m/o found
Re-test if 2nd fail due to a different m/o
Additional tests therefore increase chance of passing
140
What are pyrogens?
Endotoxins produced by the LPS of gram -ve bacteria
Project from the outer layers of the outer membrane into the surrounding environment
Lipid A component which is the endotoxin/pyrogen
141
How are pyrogens shed?
Gram -ve bacteria shed LPS/pyrogens through normal growth and division
If you are using physical means to kill cells, you will get shedding of pyrogens
142
What products must be pyrogen free?
Anything which is injectable
143
What is the LAL test used for?
Limulus amebocyte lysate (LAL) test is used for detecting endotoxins
144
What is the basis of the LAL test?
Clotting reaction of horseshoe crab lysate by endotoxin
145
What is a positive result with the LAL test?
Formation of a solid clot which withstands inversion of the tube
146
What are the 3 types of LAL test?
Gel clot - typical
Turbidometric - kinetic, rate of clotting
Colorometric - uses orange colour, increasing colouration with increasing pyrogen
147
How can pyrogens be removed from a product?
Rinsing or dilution
Heat sterilisation
Distillation
