What does testing according to ISO 11737 1/-2 mean in practice?
In practice, the combination of bioburden and sterility tests answers several key questions:
- What is the initial microbiological contamination level of my products before sterilization?
- Are the specified sterilization procedures suitable for achieving sufficient sterility on this basis ?
- Do sterilization processes remain stable over time , or do bioburden values increase (e.g., due to process changes)?
Bioburden according to ISO 11737-1
- Determination of the average germ count per product (or per defined unit)
- Selection of appropriate sample size, preparation methods (elution, filtration, etc.) and culture conditions
- Consideration of product geometry, materials and process history
- Use of bioburden data for the design of sterilization processes and for monitoring
Sterility tests according to ISO 11737-2
- Planning the testing strategy (number of samples, culture media, incubation times)
- Performing sterility tests including method validation (recovery, inhibition)
- Evaluation of positive findings to determine their causes (e.g., contamination, sampling, process deviation)
- Use of the data in the context of sterilization validation, dose determination (for EO/Gamma) and re-qualification
HygCen Germany conducts these tests under controlled laboratory conditions and documents all steps in such a way that they are traceable for authorities, notified bodies and auditors.
Standard criteria – at a glance
| Standard criterion | Requirements / Content | HygCen test |
|---|---|---|
| Bioburden determination | ISO 11737-1: Germ count per product/batch | Sampling, elution, cultivation, evaluation |
| Sterility tests | ISO 11737-2: Test design, method validation, evaluation | Sterility tests including media controls |
| Sample scope | risk-based sampling planning | Determination of the number of test samples according to standard specifications |
| Method validation | Proof that test methods reliably recover germs | Recovery and inhibition studies |
| Influence of packaging | Consideration of the sterile barrier in the test design | Sampling in/from packaging systems |
| Process monitoring | Use of bioburden/sterility to monitor sterilization | Support for requalifications |
| documentation | complete, verifiable reports | QES signed test reports |
How we test bioburden and sterility – step by step
- Clarification of product & process background:
We record:
- Product type, materials, geometry
- Manufacturing processes and, if applicable, pretreatments
- planned or existing sterilization methods (e.g. steam , EO, H₂O₂ )
- Packaging systems and storage conditions
- Result: defined test scope according to ISO 11737-1/-2.
- Test planning according to ISO 11737-1/-2
We define:
- Number of test samples (sample size)
- Sampling and preparation methods (e.g. rinsing , elution, direct exposure )
- Cultural media, incubation conditions, duration
- Parameters for method validation (recovery/inhibition)
- HygCen Germany does not decide on sterilization doses or sterilization concepts, but on the test design within the framework of the standard.
- Performing the bioburden test (ISO 11737-1)
- Sample preparation and microbiological cultivation
- Counting colony-forming units (CFU)
- Calculation of the average germ count per product
- Documentation of outliers and special features
- Performing sterility tests (ISO 11737-2)
- Incubation of the test samples in suitable media
- Observation of normal incubation times
- Method validation: Proof that potential pathogens are not suppressed by test conditions.
- Evaluation of negative vs. positive findings
- Assessment & QES-signed audit report
The report contains:
- Scope of testing, methods, standard references
- Raw data and evaluated germ counts
- Results of the method validations
- Statement on microbiological contamination and sterility under the tested conditions
- no sterilization dose specifications, no design or process advice
Why HygCen?
- DAkkS-accredited testing laboratory for microbiological testing, sterilization validation and packaging testing
- neutral, standards-compliant execution of bioburden and sterility tests
- long-standing experience with linked testing (sterilization, packaging, cleanliness, end-of-life)
- Clear distinction: no advice on sterilization strategies, only test data.
- QES-signed reports , directly usable in MDR technical documentation, requalifications and audits.
Bioburden describes the initial situation before sterilization and is therefore a key parameter for the design and evaluation of sterilization processes. Without reliable information about the number of viable microorganisms on a product, it is impossible to determine an adequate sterilization dose or to monitor the stability of the production and sterilization process. Sterility tests alone only show whether germs are detectable in the tested set of products or not – they do not replace a sound understanding of the initial bioburden.
The type of packaging and the sterile barrier significantly influence the risk of recontamination and the microbiological load before and after sterilization. A product sterilized "unpackaged" has different risks than a product in a validated packaging system according to ISO 11607-2. HygCen Germany considers both the product and the packaging system in bioburden and sterility tests, selecting the test design accordingly. Manufacturers and consultants decide whether a particular packaging is suitable for a product – we provide the test data to support these decisions.
A positive finding means that viable microorganisms were detected in at least one test sample. HygCen Germany documents this completely and impartially, including possible indications of contamination sources (e.g., sample handling, test environment, packaging damage). Assessing whether this is an "acceptable" deviation, a process disruption, or a design problem is the responsibility of manufacturers, operators, and their regulatory advisors. This often necessitates root cause analyses, additional testing, and, if necessary, re-validations.
The frequency of bioburden testing depends on risk assessment, process stability, quality management system requirements, and regulatory standards. Measurements are typically taken during the development phase, when processes or suppliers are changed, and at defined routine intervals. HygCen Germany does not set its own testing intervals but fulfills testing requests within the framework of these specifications. The bioburden data can be used to identify trends and assess whether the manufacturing and sterilization process is stable or whether adjustments are necessary.
Bioburden and sterility tests are an essential component of sterilization validation, risk management, and MDR technical documentation. They link manufacturing processes, sterilization, and packaging, providing the quantitative and qualitative evidence expected by notified bodies and regulatory authorities. Together with sterilization validation, packaging validation, end-of-life testing, and cleanliness verification, they paint a complete picture of a product's microbiological safety throughout its entire life cycle.
Further links
ISO 17664 - Validation of manufacturer's specifications, ISO 15883 - Waste Disposal Device Validation, ISO 17665-1 / EN 13060 / EN 285 - Sterilization Validation, Cleanliness Verification - TOC / Protein / Hemoglobin / ISO 19227, End of Life - Material and Functional Durability, Type Testing of Reprocessing Equipment, Packaging & sterile barrier – ISO11607-2, Reprocessing of medical devices