Determining Time
to Results
Validating an Automated Rapid Method:
with Andrew Sage Ph. D
• Background: Compendial method incubation and implications of use of RMMs
• Experimental Design Strategies for setting time to results (TTR)
• Case Study 2: EM air testing optimizing incubation profile, and TTR determination
• Summary
Overview
Background
Compendial Method Incubation Parameters and Time to Results
• Two temperatures of 22.5°C and/or 32.5°C or both serially
• Water testing: 32.5°C, 3 D (USP) > 5 days (EP)
• Higher temperature, longer incubation allow growth of oligotrophic, possibly stressed water species
• Bioburden: Single temperature (22.5°C or 32.5°C): 3-5 D (USP, EP)
• Lower or higher temperature allows mold/yeast or bacteria to be more effectively recovered
• Environmental Monitoring (air & surfaces, personnel): serial incubation –
• 22.5°C (3-5 D), 32.5°C (2-3 D) (WHO, EMA)
• Low to high or high to low temperature shift will allow mold/yeast and bacteria both to be detected
• Low to high allows temperature sensitive molds to develop – but they may then over grow bacteria
• High to low allows bacteria to develop and be counted before mold can develop with the lower temperature incubation
• Alternate incubation regimes used:
• Example: Single temperature for EM of 28°C
• Presume that this temperature will support growth of mold and bacteria equally
Implications of Use of RMMs
• Use of RMMs are meant to reduce Time-to-Result of testing
• Results to be as good or better than current test method (i.e. accuracy, precision, LoD etc.)
• Important that RMMs provide time savings that are worthwhile for ROI for user
• Different technologies are available – each comes with pluses and minuses (read the fine print)
• Real time detection: Answer is immediate, but there is no colony to count or isolate to ID
• Complicates comparison to compendial method, tracking of facility bioburden
• Growth based: Longer TTR, but there is a colony to identify for tracking
• Both must be shown to proide accurate results vs. the compendial methods
Pitfalls of a Wrong TTR Selection
• Time to Result is selected to balance need for accuracy with need for a timely answer
• Compendial time to results are recommended to essentially balance these needs
• One can often incubate longer, at another temperature and recover more or different colonies
• With RMM, must also balance between a faster answer and accuracy
• Wrong TTR can have serious results:
• Too short: possible missed contamination and possible tainted product
• Too long: lose any advantage to use the RMM
• For growth-basedRMMs, TTR needs to be determined and then confirmed by equivalence testing
• Non-growth based (e.g. epiflourescence not applicable)
Performing TTR Determination
• Requirements for determining growth-based TTR
• Need a regular, if not continuous analysis of growth
• Need an assay method that is non-destructive
• To simplify the process, need a system that:
• Performs automated, non-destructive analysis of colony numbers
• Analysis to be at measured intervals during incubation
• This discussion uses the Growth Direct™ System for the case study presented (process is applicable to any such system)
• Growth-based detection
• Automated sample handling
• Non-destructive detection technology
The Growth Direct™ Technology Platform
TTR Process Simplified by Automation
• Use of automated, non-destructive system simplifies TTR determination
• Automation allows analysis to be performed at measured times, on schedule at all hours without interruption
• Difficult to perform without automation
• Need really dedicated lab personnel
• A non-destructive assay allows repeated analysis of the same sample
• Final count at end of incubation as defined by standard method
• Impossible to perform with destructive tests
Experimental Design Strategies
for Setting TTR
Flow Chart for TTR Determination
Define protocol method
Define test organisms and/or
samples
Run Experiments Analyze Data
Equivalence TestingSet presumptive
TTR
Complete
Flow Chart for TTR Determination
• Compare detection of time course of standard incubation vs. final count
• Set test samples:
• In-house isolates associated with process or environment
• Samples from the process environment
• If needed, prepare stressed populations that will reflect environment of sample source
• Product matrix (e.g. pH osmiarity
• Clean room (e.g. disinfectant, bleach treatment)
• For single incubation run RMM on same media, temperature as reference method
• Run for the full time of compendial or standard method
• First time point at which RMM is >70% detection for all the test organisms over the course of the reference incubation can be selected as TTR
• May add time to ensure >70%, or other considerations
• Can focus on specific frame based on vendor claims (for example ~50% of standard method)
• For serial incubation (case study)
• Run RMM at same temperature profile and media
• Minimum time of compendial or standard method of each temperature
• Use vendor claims (e.g. ~50% of standard method)
• First time point where RMM is >70% of reference at the end of the serial incubation can be defined as TTR
Case Study: Determining Best Incubation Profile and
TTR for Air Testing
Goal: Determine optimal incubation profile and TTR for an active air testing application
Questions to answer during this study:
• What is the best incubation profile for optimal detection of microbial contaminants?
• With the selected profile, determine the Time-to-Result (70% of total count)
• Does the selected TTR provide results that are comparable to the standard method
Background
• Environmental monitoring (air, surfaces, personnel) can be performed using single or serial incubation
• Single incubation: 22.5°C or 32.5°C
• 22.5°C presumed good for molds, 32.5°C for bacteria
• To recover both – run 22.5°C and 32.5°C serialy
• Questions to answer during this study:
• Is single incubation sufficient?
• If serial, do 32.5°C first or 22.5°C first
• How long an incubation for each temperature?
• What TTR to select for the chosen incubation profile?
Samples for Testing
• For incubation profile and TTR determination
• Isolated from EM air testing in dirty environments
• Range of fast and slow-growing strains
• Mold and bacterial species
• No real world samples
• Equivalence testing: Growth Direct™ vs. standard method in air testing in facility
• Real world samples compared over time
Procedure
• Based on ~50% TTR claim for time to result, all strains should be detected within 4 days on system –run 96th
• 1st: What is optimal incubation profile?
• Is serial really the best method?
• Test detection of colonies at different incubation parameters:
• 22°C, 96 hours
• 22°C, 96 hours, 48 hours followed by 32°C, 96 hours 48 hours
• 32°C, 96 hours, 48 hours followed by 22°C, 96 hours 48 hours
• 32°C, 96 hours
• 2nd: What is TTR at optimal incubation profile
• Compare detection vs. final count of test organisms
• 3rd: Confirm TTR is appropriate in side-by-side
EM Isolate Detection Curves at 4 Profiles: Bacteria
32°C provides faster detection for bacteria
EM Isolate Detection Curves at 4 Points: Molds
32°C prevents recovery of some mold species. Need 22°C first for mold recovery
TTR Determination at Incubation Profile
22 C, 48 hr; 32 C, 48 hr
Selected incubation profile provides about 50% shorter TTR
TTR 70%, ~60 hr
Equivalence Testing: Co-Trending of Air Samples
Equivalence testing shows co-trending of RMM result and control standard method
Considering Alternative Strategies
• Additional option: one can optimize TTR for a RMM using an alternate testing strategy
• With new method, can look to improve testing
• Example: air testing TTR
• 22°C and 32°C alone are not effective
• Move to 28°C for single incubation?
• Advantages of single temperature
• For RMM, higher throughput
• Possible reduced TTR
• Lower resource uses
Alternative Incubation (28 C) TTR
Possible obtain same TTR and reduce resource use
TTR 70%, ~56 hr
70% detection
Using Real World Samples
• Use of real world samples in problematical
• Great to use if possible
• Provide microbes in appropriate physiological state (stressed)
• Sampling a good
• Most samples have limited or no contamination
• Clean rooms for EM, final product for bioburden/sterility – Difficult to use
• In-house isolated obtained during normal testing can be treated to mimic stress of environment
• Mimic stress state that exists for real world samples – Examples:
• Surfaces – treat with antimicrobial compounds used in clean room
• Water testing – expose in-house isolates to same water to induce nutrient, osmotic stress
• Final product – expose test organisms to product matrix or active antimicrobial ingredients
• Provide an approximation of the response of organisms from the test environment
Summary
• As with any technology, growth-based RMMs must be validated. A part of the process can involve selecting and confirming a Time-to-Result for the RMM
• Automated, non-destructive platforms provide the means to most effectively carry out experimentation to set and validate a Time-to-Result
• The basic strategy for setting TTR is to determine at which point comparable recovery of microbial test samples is obtained vs. the normal reference method
• Test samples can be in-house or real world samples
• Isolates treated to approximate the stress state of the sample matrix can also be used
• Selected TTRs should be confirmed by side-by-side equivalency testing
• TTR selection may be influenced by other factors such as personnel availability
• Setting TTR was illustrated by determining the optimal incubation profile, and time-to-result for environmental air sample testing on the Growth Direct™ System using in-house EM isolates
• The effectiveness of an alternate incubation strategy was also shown by determination of the TTR using a subset of the same test organisms
Contact Us Today
Are you ready to automate your QC Micro testing?
Phone: 781-271-1444For General Information: [email protected]
For Sales and Product Inquiries: [email protected] Technical Inquiries: [email protected]