Bioburden Testing for Medical Devices (ISO 11737‑1 & USP <61>)
Key Highlights
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Bioburden testing measures the number of live microorganisms on a medical device before it goes through sterilization. This information is essential because it helps set the right sterilization method and confirms that the manufacturing process stays clean and under control.
At North American Biomedical Institute (NABI), we perform bioburden testing in GLP-certified, ISO 17025-accredited, and FDA-compliant laboratories. Our team specializes in microbiology and sterility testing under ISO 11737. We support medical device companies through every stage of development and validation.
What is Bioburden Testing?
Bioburden is the total number of live microorganisms (bacteria, yeasts, or molds) found on a medical device before sterilization. These microorganisms come from raw materials, handling, and the manufacturing environment.
Bioburden testing is a quantitative microbiology test that measures this level of contamination. Results are usually expressed as CFU per device or CFU per milliliter, depending on the product and extraction method.
Bioburden testing is not the same as sterility testing. Bioburden testing measures how much contamination is present before sterilization, while sterility testing confirms that no viable microorganisms remain after the device has been sterilized.
When Do You Need Bioburden Testing?
New Device Sterilization Validation
Bioburden testing is required when you validate a new sterilization process. This includes gamma, e-beam, EO, and steam sterilization. Testing shows the starting microbial load, so you can select the right sterilization method.
Radiation and EO Dose Setting
Bioburden results help set and verify the sterilization dose. They support ISO 11137 for radiation and ISO 11135 for EO sterilization. This step confirms the chosen dose can reach the needed Sterility Assurance Level.
Routine Process Monitoring
Many manufacturers run bioburden testing on a routine schedule. This may be quarterly or based on risk. The goal is to track trends, confirm the process stays under control, and support sterilization dose audits.
Changes in Materials or Suppliers
You may need bioburden testing when you change materials, switch suppliers, adjust cleaning steps, or modify packaging. Any shift in the process can affect microbial load.
Contamination or Sterility Failures
Bioburden testing is also used during investigations. It helps find the source of unexpected contamination and guides corrective action after a sterility failure.
Standards & Regulatory Expectations
Bioburden testing follows several key standards and guidelines. These documents explain how to measure microbial load and how to use the results in a sterilization validation.
ISO 11737-1:2018
ISO 11737-1 is the main standard for bioburden testing. It explains:
- how to choose sample plans
- how to extract microorganisms from a device
- how to measure recovery efficiency
- how to evaluate the results
This is the foundation for most medical device bioburden studies.
USP <61>
USP <61> covers microbial enumeration tests for non-sterile products. It aligns with Ph. Eur. 2.6.12 and 2.6.13. These tests may apply when a device uses pharmaceutical raw materials or when the product must meet both device and drug standards.
ISO 11137 and ISO 11135
Bioburden data is a key part of radiation and EO sterilization validations.
- ISO 11137 guides radiation sterilization dose setting and dose audits.
- ISO 11135 guides EO sterilization validation and routine control.
Both rely on accurate bioburden results to confirm that the sterilization process achieves the required Sterility Assurance Level.
FDA Expectations
The FDA recognizes ANSI/AAMI/ISO 11737-1 as a consensus standard. It also expects manufacturers to understand and control product bioburden as part of their sterilization process controls.
Clear bioburden data support 510(k) submissions, PMAs, and routine quality system reviews.
What NABI’s Bioburden Testing Covers
Typical Products
We support a wide range of medical devices and materials that need bioburden control and clean manufacturing.
Single-use and reusable medical devices are tested to confirm the microbial load on both implantable devices and external-use products.
Device components and sub-assemblies include parts, molded pieces, tubing sets, and other pieces that become part of the final device.
Device packaging and sterile barriers are evaluated, including trays, pouches, and barrier systems that need to meet ISO 11607 requirements.
Raw materials used in device manufacturing, such as polymers, elastomers, and tubing, are tested when microbial load may affect the final product.
Organisms & Test Types
Bioburden testing focuses on the types of microorganisms that may be present on a device before sterilization. The core test looks at common, easy-to-grow organisms, and additional organisms can be included when the device’s risk profile requires it.
Baseline organisms measured:
- Aerobic bacteria
- Yeasts
- Molds
Additional organisms when needed:
- Spores
- Anaerobes
Results are reported as total viable count (CFU), and we can also include basic information on the types of microorganisms present upon request.
NABI Bioburden Testing Workflow (ISO 11737-1 Compliant)
Our workflow follows ISO 11737-1 and is designed to give clear, reliable results. Each study starts with careful planning, moves through structured lab work, and ends with data you can use in your sterilization validation.
Study Design & Planning
We begin by reviewing the device and how it will be used. This includes:
- device type
- planned sterilization method
- required Sterility Assurance Level
If you have past data, we look at that too. Short reviews like this help us choose the right test setup.
Next, we build a sampling plan. We decide how many units to test, how many lots to include, and the time points needed. This plan follows ISO 11737-1 and supports your overall sterilization validation.
Sample Preparation & Microbial Extraction
We prepare each device in a way that keeps the test clean and controlled. Devices may be cut, opened, rinsed, or flushed, depending on their design. All steps are done aseptically to prevent outside contamination.
To remove microorganisms from the device, we use extraction methods that fit the material and shape:
- Mechanical shaking or vortexing
- Sonication
- “Stomaching” for soft or flexible materials
We choose an extraction medium that supports good recovery. This may be a simple buffered solution or a buffer with a mild surfactant. The goal is to lift organisms from the device without harming them, so the final count is accurate.
Plating, Incubation & Enumeration
After extraction, the sample is prepared for counting. When the liquid is clear enough, we use membrane filtration. The membrane is placed on growth media and incubated at different temperatures to support both bacteria and fungi.
If the extract has debris, gels, or too many particles, we use pour plating instead. This method mixes the sample with warm agar so colonies can grow throughout the plate.
For samples with very low bioburden, we may use the Most Probable Number (MPN) method. This approach helps detect low levels of microorganisms when standard plating is not sensitive enough.
Data Interpretation & Reporting
We report bioburden as CFU per device or CFU per sample, depending on the study design. Each report includes the incubation conditions used, so you can see how bacteria and fungi were grown. If you request organism information, we can also note the basic types of microorganisms found.
We review the results for patterns or changes over time. If we see shifts in counts or in the types of organisms present, we flag them. These changes can affect sterilization dose, SAL targets, and overall process control, so clear trend insight is important.
Method Validation & Recovery Efficiency
ISO 11737-1 requires every bioburden method to be validated. This step confirms that the method can recover microorganisms from the device and that nothing in the product or extraction fluid blocks their growth. Good recovery makes the final count reliable and defensible.
There are two main ways to show recovery efficiency:
- Exhaustive extraction, where the device is extracted multiple times until no more organisms appear.
- Product inoculation, where known organisms are added to the device, recovered, and measured.
At NABI, this work is usually completed as a separate bioburden recovery factor study. The results set the recovery factor used in routine bioburden testing and ensure that every test follows ISO 11737-1 expectations.
Frequency & Sample Size: Building a Risk-Based Program
ISO 11737-1 does not set a fixed schedule for bioburden testing. Instead, it expects each manufacturer to choose a frequency based on historical data and a clear, documented rationale. The goal is to test often enough to confirm that the process stays under control without adding unnecessary work.
Many teams start with more frequent testing during validation or early production. This helps establish a baseline and catch issues early. Once the process shows stable trends, testing often shifts to quarterly or semi-annual intervals.
Sample size can also change based on risk. Key factors include:
- target SAL
- complexity of the product
- environmental controls
- size of each batch
Higher-risk products may require more units or more lots to get an accurate picture.
NABI can help you design or justify your sampling plan as part of a full microbiology and sterilization strategy.
How Bioburden Testing Connects to Sterility & Other NABI Services
Bioburden testing supports several downstream microbiology and sterilization steps. It shows the microbial load on a device before sterilization and helps confirm that later tests are accurate and reliable.
Bioburden results feed directly into product sterility testing under USP <71>. This connection helps demonstrate that the sterilization process achieves the needed sterility level and that the final device is safe for use.
Bioburden data also links to Bacteriostasis & Fungistasis (B&F) testing. B&F testing checks that the product does not inhibit microbial growth in the sterility test media, which helps prevent false-negative results.
For reusable medical devices, bioburden supports cleaning and reprocessing work. It plays a role in steam sterilization validation for reusable medical devices by confirming that cleaning steps and sterilization cycles remain effective over time.
Why Work with NABI for Bioburden Testing?
NABI stands out because our microbiology work is built on strong quality systems, deep device expertise, and a full-service approach that supports fast, reliable submissions.
GLP and ISO 17025 Laboratory Quality
Our labs are GLP-certified and ISO 17025-accredited, and we operate under FDA 21 CFR 58.
These standards match what ISO 10993 and global regulators expect when bioburden results support a submission.
Part of the Biomedical Institutes Group
NABI is part of the Biomedical Institutes Group, alongside the European Biomedical Institute (EBI).
This gives you access to global expertise, unified systems, and a team focused on medical device testing.
Experienced Microbiology and Biocompatibility Team
Our team includes microbiologists, chemists, and in-house toxicologists.
We work with FDA and MDR expectations every day and understand how bioburden results fit into your overall safety and regulatory strategy.
Integrated Testing Capabilities
We can connect your bioburden testing with biocompatibility, chemistry, EO/ECH residual testing, and other required studies.
This reduces delays, keeps projects aligned, and helps you move through validation and submission with confidence.
Turnaround, Samples & What to Send
Turnaround Time
Turnaround time depends on the type of study and what the device needs.
Routine bioburden tests are often faster, while studies that require method development or validation take longer.
The number of samples, the types of organisms tested, and the incubation periods also affect timing. We review these details at the start of the project and give a clear estimate based on your study plan.
Sample Requirements
Most studies require at least three non-sterile samples to begin. The exact number depends on whether the test is part of validation work or routine monitoring. Below is a general guide:
Initial validation studies:
- 3–10 samples per configuration
- Multiple lots when possible
- More units may be needed for recovery efficiency or method development
Routine monitoring:
- 3–5 samples per lot
- Counts may increase if the process is new or if trends change
To protect sample integrity, devices should be packaged so they stay clean and dry. Use sealed, non-shedding packaging and place samples in a way that prevents damage during shipping.
If the device contains fluids or gels, cushion it to avoid leaks or pressure changes in transit.
Information Checklist
A few details help us design the study and choose the right test plan. The list below covers what most projects need:
- Device description and device classification
- Intended sterilization method and the target SAL
- Key materials and an outline of the manufacturing flow
- Any known microbiological concerns, such as environmental flora or past excursions
If you’re unsure what to send, contact us and our team can guide you through the requirements.
FAQs About Bioburden Testing
What is a bioburden test for medical devices?
A bioburden test measures the level of microbial contamination on a device before sterilization. It confirms that the device meets regulatory expectations and that the sterilization approach is appropriate. Bioburden testing is required for all sterilization validations and for most regulatory submissions.
What’s the difference between bioburden testing and sterility testing?
Bioburden testing measures how many microorganisms are on a device before sterilization. Sterility testing confirms that no viable microorganisms remain after the validated sterilization cycle.
Which standards apply to bioburden testing for my medical device?
Bioburden testing follows ISO 11737-1, which covers sampling, extraction, recovery, and data evaluation. Depending on the sterilization method, results may also support ISO 11137 (radiation) or ISO 11135 (EO).
When pharmaceutical materials are involved, USP <61> microbial enumeration tests may apply. The FDA recognizes ANSI/AAMI/ISO 11737-1 as a consensus standard.
How many samples do I need for bioburden testing?
ISO 11737-1 does not set a fixed number. Sample size depends on risk, product complexity, and the sterilization method. Typical ranges include 3–10+ samples per lot for dose audits or new validations, and 3–5 samples for routine monitoring.
Can you help design a bioburden monitoring plan for FDA or MDR compliance?
Yes. NABI can create a risk-based monitoring plan that aligns with FDA and MDR expectations and fits your device, workflow, and submission strategy.
How long does bioburden testing take?
Timing depends on incubation requirements and whether method validation is needed. Bacteria and fungi usually need several days of incubation. If the method must be validated first, the timeline will increase. We provide a clear estimate once the study plan is set.
What are the main methods used in bioburden testing?
Bioburden testing often uses two core methods:
Membrane filtration:
Used when the extract is clear enough. The liquid is filtered, the membrane is placed on growth media, and colonies are counted.
Plate count methods (pour or spread plate):
Used when filtration is not possible, such as when the sample has debris or gels.
Both methods include incubation and final CFU counts to measure microbial load.
How often should bioburden testing be done?
Frequency depends on risk. New products often use more frequent testing during validation. Stable processes may use quarterly or semi-annual testing. Your monitoring plan should be supported by data and documented reasoning.