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Understanding CAN/CSA-ISO 11138-5:17 – Biological Indicators for Ethylene Oxide Sterilization Processes
Technical Requirements, Performance Validation, and Compliance Strategies for Low‑Temperature Sterilization Assurance
1. Scope and Overview
CAN/CSA-ISO 11138-5:17 is the Canadian adoption of ISO 11138-5:2017, Sterilization of health care products — Biological indicators — Part 5: Biological indicators for low‑temperature sterilization processes using ethylene oxide (EO). This standard specifies the requirements for biological indicators (BIs) intended for use in EO sterilization cycles that operate below typical thermal sterilization temperatures. It is part of the ISO 11138 series, which provides a consistent framework for BI design, production, and performance evaluation across different sterilization modalities.
The document applies to BIs that contain viable microorganisms (typically spores) with a defined resistance to ethylene oxide. It establishes the minimum performance criteria necessary to ensure that the BI can be used to monitor, validate, and release EO sterilization processes in healthcare, pharmaceutical, and medical device manufacturing environments. The standard harmonizes with Good Manufacturing Practice (GMP) principles and regional regulatory requirements, facilitating global acceptance of sterilization validation data.
Note: CAN/CSA-ISO 11138-5:17 is identical to ISO 11138-5:2017. Users should consult the latest editions of both the base standard and any national deviations published by the Standards Council of Canada.
2. Technical Requirements and Performance Criteria
2.1 Biological Indicator Design and Components
Each BI must be a self-contained test system comprising an inoculum of bacterial spores applied to a carrier, enclosed in a primary package that is permeable to ethylene oxide and moisture. The standard requires that the carrier material and packaging do not interfere with spore viability or the sterilization process. A complete BI also includes a growth medium (e.g., soybean casein digest medium) that supports recovery of viable spores after exposure, unless the BI is intended for transfer to separate culture media.
2.2 Test Organism and Inoculum
The standard mandates the use of Bacillus atrophaeus (formerly Bacillus subtilis var. niger) ATCC 9372 or a strain with demonstrably equivalent resistance. The spore population on each BI shall be homogeneous and within a specified range (typically 1×10⁵ to 1×10⁶ colony forming units per carrier). The manufacturer must document the spore preparation method, purity, and resistance spectrum.
2.3 Resistance Characteristics (D-value and Survival/Kill Windows)
The D-value (time required to reduce the viable spore population by one log10 under defined EO exposure conditions) is the critical performance parameter. For EO sterilization at a defined set point (e.g., 600±30 mg/L EO, 54±1 °C, 60±10% RH), the D-value must be determined according to Annex A of ISO 11138-5. The standard also specifies survival and kill windows — exposure times that must yield no growth or complete kill, respectively. These windows confirm that the BI exhibits consistent resistance.
| Parameter | Requirement | Test Method (ISO 11138-5) |
|---|---|---|
| Spore population (CFU/carrier) | ≥ 1×105 and ≤ 1×106 | Plate count or membrane filtration |
| D-value at reference conditions | ≥ 2.5 min and ≤ 6.0 min | Annex A (survivor curve analysis) |
| Survival time (no growth) | ≥ 2× D-value (e.g., ≥ 5.0 min for D=2.5 min) | Direct incubation after defined exposure |
| Kill time (all negative) | ≤ 4× D-value (e.g., ≤ 10 min for D=2.5 min) | Direct incubation after defined exposure |
| Purity and morphology | Typical Gram‑positive sporeformer, single colony type | Microscopy and subculture |
2.4 Subculture and Growth Conditions
After exposure to ethylene oxide, the BI is incubated in the appropriate growth medium at 30–35 °C for 7 days. The standard defines the incubation temperature range and requires that the medium supports recovery of even sub‑lethally injured spores. Growth must be read against a known negative control (uninoculated medium) and a positive control (unexposed BI).
2.5 Shelf Life and Storage Conditions
The manufacturer must assign a shelf life based on real‑time stability studies. The standard recommends storage at 2–25 °C away from direct sunlight and ethylene oxide sources. Any degradation beyond permissible limits (e.g., D-value shift >10%) over the stated shelf life renders the batch non‑compliant.
Important: Users must verify the D‑value and spore count for each lot upon receipt, especially when BIs are transported under uncontrolled conditions. Discrepancies should be reported to the manufacturer and may invalidate sterilization cycle validation data.
3. Implementation Considerations
Selecting the appropriate BI model involves matching its D‑value, spore population, and packaging to the specific EO cycle parameters (gas concentration, temperature, humidity, and exposure time). Healthcare facilities and device manufacturers should:
- Procure BIs from suppliers whose quality management system is certified to ISO 13485 or equivalent.
- Maintain a lot‑specific calibration certificate stating the D‑value and spore count performed per ISO 11138-5 test methods.
- Perform routine quality control testing by incubating a negative control and a positive control alongside every test BI batch.
- Document all BI test results as part of the sterilization cycle release criteria.
When adopting CAN/CSA-ISO 11138-5:17, Canadian users should also consult Health Canada’s guidance on sterilization validation and any provincial regulatory nuances.
Best Practice: Use BIs placed in the most challenging locations (process challenge devices) to represent the worst‑case sterilization conditions. This enhances the robustness of the validation effort.
4. Compliance Notes
Compliance with CAN/CSA-ISO 11138-5:17 is not mandatory unless referenced by a regulatory authority or contractual agreement. However, the standard is widely recognized as the benchmark for EO sterilization biological indicators. Key compliance points include:
- Traceability: Each BI lot must be traceable to its production batch, including raw materials and spore master seed lot.
- Testing: Manufacturers must perform routine quality control (D‑value, spore count, survival/kill windows) at defined intervals.
- Documentation: Instructions for use, storage, and disposal must accompany each shipment, in both official languages for Canada.
- Expiry: The labeled shelf life must be supported by stability data in accordance with ISO 11138-1 (general requirements for BIs).
Non‑conformance can lead to false‑positive or false‑negative biological indicator results, compromising sterility assurance. Regulatory bodies such as Health Canada may cite deviations from recognized standards during inspections.
Critical: Never reuse a biological indicator. Each BI is designed for single‑use only. Reusing an exposed BI invalidates the test and can introduce false negatives due to spore recontamination or degradation of the growth medium.
Frequently Asked Questions
Q: What is the primary test organism specified in ISO 11138-5?
A: Bacillus atrophaeus ATCC 9372 (formerly Bacillus subtilis var. niger). Manufacturers may use an equivalent strain only after demonstrating that its resistance characteristics match those of the reference strain under the defined EO conditions.
Q: How is the D‑value determined for an ethylene oxide biological indicator?
A: The D‑value is determined by the survivor curve method described in Annex A of ISO 11138-5:2017. BIs are exposed to a reference EO cycle at increasing time intervals, the viable spores per carrier are counted, and the log10 reduction is plotted against exposure time. The D‑value is the negative reciprocal of the slope.
Q: What are the typical storage conditions for EO biological indicators?
A: The standard recommends storage at 2–25 °C in a dark, dry environment. Avoid exposure to EO gas, high humidity, and extreme temperatures, which can alter the resistance characteristics of the spores.
Q: Can biological indicators from other sterilization standards (e.g., ISO 11138-3 for moist heat) be used for EO validation?
A: No. Each ISO 11138 part addresses a specific sterilization process with a designated test organism and resistance profile. BIs for EO must conform specifically to ISO 11138-5; using BIs intended for steam, dry heat, or vaporized hydrogen peroxide will provide invalid results for EO cycle validation.
Article prepared based on the requirements of CAN/CSA-ISO 11138-5:17 (identical to ISO 11138-5:2017). All technical data should be verified against the latest edition of the standard. This article is for informational purposes and does not substitute for the full normative document.
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