For cell and gene therapies (CGT) and other advanced therapy medicinal products (ATMPs), sterility testing presents a particular challenge. Many therapies have short shelf lives and cannot be terminally sterilised, while conventional compendial sterility testing can require up to 14 days. Rapid microbiological methods are increasingly used to shorten testing times, but combining rapid results with the benefits of growth-based detection has, until now, remained a challenge.
Symcel is addressing this by utilizing the principle of biocalorimetry and isothermal microcalorimetry (IMC) technology to develop dedicated sterility testing systems designed to provide growth-based sterility testing results within three days.
Two complementary sterility testing systems, calScreener+ and caloTrace have been developed based on the same platform. The calScreener+ is a benchtop system for smaller volume testing and method evaluations. The caloTrace is a further development scaling the platform to larger-volume testing and automation. Both units are designed to detect very low levels of microbial contamination as early as possible while maintaining the fundamental principles and benefits of compendial sterility testing.
Continuous development and optimization have not only expanded the operational capabilities of the technology, but also progressively reduced the time required to detect microbial growth.
Detection of all USP compendial organisms within 36 hours.
The assay-limiting organisms C. acnes now detected in approximately 48 hours
This opens the door to a new generation of sterility testing, retaining the benefits of growth-based detection and regulatory alignment while substantially shortening sterility test release times.
Achieving this has required optimization not only of the detection technology, but of the entire microbial growth environment.
IMC technology is based on continuous detection of the heat generated by microbial metabolism, enabling label-free detection of viable and growing microorganisms.
Sterility testing requires the detection of contamination originating from only a few microorganisms, potentially with very different growth characteristics. The assay therefore needs to support rapid and reliable recovery and growth from very low starting concentrations.
At the same time, retaining FTM and TSB has been an important consideration for maintaining alignment with established compendial sterility testing methods. Development has therefore focused on optimising the growth conditions around these established media to enable faster detection across a broad range of microorganisms, including compendial strains, environmental isolates and challenging slow-growing organisms.
While many microorganisms can generate a detectable signal within hours, slow-growing anaerobic organisms can determine how early a sample can confidently be reported as negative. Particular attention has therefore been given to Cutibacterium acnes, with its increased detection speed being an important step towards achieving negative sterility results within 2–3 days.
Microbial growth is influenced by more than culture media. Development has therefore focused on optimizing the complete growth environment within a closed-vial system, with direct sample inoculation through the septum. Sample volume, media volume, vial geometry and headspace all contribute to the conditions experienced by the microorganisms.
The liquid-to-headspace ratio, for example, affects gas availability and can influence the growth of both aerobic and anaerobic organisms. These parameters therefore become part of assay optimisation rather than simply characteristics of the test container. Together, they form an integral part of creating the environment that has enabled rapid detection times.
The larger 13.5 mL caloTrace vials have not only expanded the user flexibility to test more sample in each vial, the larger caloTrace volume has also meant increased possibilities to even further optimize the sample-media test environment. This has contributed considerably to pushing time to detection even further with caloTrace.
Speed is only meaningful if sensitivity is maintained. This balance between sensitivity and speed has therefore been central to the development of calScreener+ and caloTrace, enabling a 1 CFU limit of detection while progressively reducing time to detection.
Achieving this starts with the ability to detect very small amounts of heat generated during the earliest stages of microbial growth. The use of highly sensitive Peltier-based sensors has therefore been a key part of the instrument development, enabling increasingly small metabolic signals to be captured.
In parallel, extensive testing at low inoculation levels across different microorganisms has been used to optimize assay conditions and establish reliable recovery and detection at concentrations approaching the single-CFU level.
Ultimately, an optimized sterility testing system depends on bringing microbiology and technology together. The breakthroughs achieved with calScreener+ and caloTrace have come from developing both in parallel, bringing together the deep microbiological expertise of the Clinical Development team with the broad sensor, mechanical and software competence of the R&D team. The journey continuous and optimization is now focused on pushing detection speeds of all USP compendial organisms down to 24 hours.
Learn more about calScreener+ Sterility, caloTrace Sterility and advanced therapies and biologics sterility testing solutions
Contact us at sterility@symcel.com to discuss your application and how IMC technology can support your sterility testing.