Sterilisation Processing Flashcards
What are the 2 approaches to making sterile products?
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’
What are some sources of microbial contaminants within the manufacturing environment?
Raw materials
Operators
Equipment and facilities
Water and air as vectors
Why are raw materials more of a worry when considering microbial contaminants?
Natural materials have a greater range of microbes vs. synthetic or semi-synthetic materials
M/o normally found in a particular environment are referred to as what?
Resident
What happens when a contaminant is found in the manufacturing environment?
Identified by genus and species
Identification can indicate the source since different environments are characterised by different microbes
What m/o are found in soil?
Endospore producing
Fungi
Mainly gram +ve
What m/o are found in water?
Gram -ve (due to cell wall structure)
Yeasts and moulds
What m/o are found in animals/humans?
Gram +ve/-ve
Obligate anaerobes
Dependent on touch transfer, personal hygeine, sneezing, coughing etc.
What m/o are found in plants?
Yeasts and moulds
What are transient organisms?
Those that are shed in one place and are carried by vectors (air, water, operators) to another site
Define ‘sterile’
Free of viable microorganisms
An absolute term, something cannot be ‘quite’ sterile
Define ‘sterilisation’
Killing or removal of all viable microorganisms
What are the traditional methods of sterilisation processing?
Killing e.g. radiation, heat (moist/dry), chemical (EtO)
Complete removal e.g. filtration
All sterilisation processes are governed by what?
A set of international standards for consistency e.g. EN, FA and Japanese
Standards provide guidance on what?
Validating sterilising agent
Validating sterilisation process
Monitoring sterilisation process
Control of m/o in the manufacturing environment
How is sterilisation assessed?
By measuring the rate and degree of kill of a microorganism
How can a kill curve be calculated?
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
How can we count the no. of viable m/o’s present without knowing how many we’re starting off with?
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
How can data from a kill curve experiment be represented?
Table
Graph preferred
What are the axis on a kill curve graph?
No. of survivors on the y-axis
Time on the x-axis
What can be said about the kill curve graph? (shape, usefulness)
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)
How can the kill curve graph be altered to help us make more sense of the data?
Semi-logarithmic version can be plotted
Gives a linear relationship allowing us to calculate gradient
What does the gradient of a semi-logarithmic kill curve graph equal?
Thermal death rate - how quickly m/o dies at a particular temperature
The higher the temperature an organism is exposed to (kill-curve graph)?
The steeper the gradient and the faster the rate of kill
Applies to examples other than temperature (EtO, radiation)
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
Define D-value
The time taken, at a fixed temperature, to reduce the population by 90% or 1-log cycle
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
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
Define Z-value
The temperature change required to produce a 90% or 1-log cycle reduction in D-value
For which type of sterilisation is Z-value applicable?
Heat only
How is Z-value calculated?
Plot of log D value against temperature
Z-value can be described as a measure of what?
Thermal resistance
Z-value can be described as an indicator of what?
Efficacy
What needs to be done in order to make sense of Z-values?
Comparison to a reference set of standards
What is the standard BI for moist heat sterilisation?
What is its Z-value?
Bacillus stearothermophillus endospores
10ᵒC
What is the standard BI for dry heat sterilisation?
What is its Z-value?
Bacillus subtilus endospores
20ᵒC
What does a Z-value of 10ᵒC mean?
For every 10 degrees increase in temperature, there is a 90% reduction in D-value
Why are these standard BI’s for Z-value comparison chosen?
Constant resistance
Endospores are the most resistant form
What is the sterility assurance level? (definition)
Minimum value to which all sterilisation processes must adhere, but most aim beyond this
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
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
Define ‘bioburden’
A population of viable microorganisms on or in a product/package
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
Time to SAL is influenced by what 3 factors?
D-value
Initial bioburden
Time of heating
D-values are influenced by what 5 factors?
Vegetative/endospore Bacterial species Production method Nutrient environment Treatment dose
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
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)
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
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
Define CFU
Colony forming units, total no. of cells
How can you decide which culture condition is best?
That with the highest CFU and greatest variety of organisms (highest no. of colony types)
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
What does process validation involve? (2)
Installation qualification
Performance qualification
What does performance qualification involve? (2)
Physical quantification
Microbiological qualification
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
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
What is a downside to microbiological quantification?
Because they’re biological, they are more prone to error and variability, changes in genotype etc.
Define ‘biological indicator’
An inoculated carrier contained within its primary pack ready for use and providing a defined resistance to the specified sterilisation process