Microbiological Ingress Testing
Microbial Ingress/Barrier testing is the evaluation of the ability of a medical device to resist or inhibit the transfer of infectious microorganisms. This is recognised as a key feature in several national and international standards where medical devices are intended to provide a barrier to the spread of infective agents to and from patients.
Syringe Integrity Testing
Disposable syringes with closure mechanisms are regularly used as final containers for aseptic products prepared within hospital units. It is essential that the syringe system maintains microbiological integrity until used. SMTL offer the microbiological integrity test from the protocol developed by the NHS Pharmaceutical Quality Assurance committee.
The principle of the test is to fill the syringe system with sterile nutritive media (performed by trained technicians in an aseptic pharmacy unit), the outside of the syringe is then challenged with an actively growing microorganism (Brevundimonas diminuta, a small motile rod-shaped bacterium) to assess container integrity. The test consists of three parts:
- The whole immersion test where the whole syringe is submerged in broth.
- The partial immersion test where the plunger/ barrel interface is challenged.
- The partial immersion test where the hub/ Luer connector fitting is challenged.
The syringes are pre-incubated to confirm the aseptic fill has been carried out correctly and the contents are sterile. The challenge organism is then introduced, and the syringes are incubated with for 14 days. The integrity of the syringes plunger or hub system is confirmed providing that the broth in all syringes remains free from microbial growth.
SMTL have modified the partial immersion test where the plunger/ barrel interface is challenged to ensure that sufficient broth remains (down the barrel) after the incubation period, the syringe is only filled to half the maximum fill volume.
SMTL have previously published test reports on the use of this test for ISO 80369-6 neuraxial syringes as part of the NHS Wales contracting process.
Relevant Standards
- NHS Pharmaceutical Quality Assurance Committee Microbiological Protocol for the Integrity Testing of Syringes
Bacterial Barrier Testing
Wound dressings should be permeable to oxygen and water vapour but impermeable to microorganisms to promote optimum wound healing and prevent infection. Efforts have been made to develop a European Standard to assess the bacterial barrier properties of wound dressings, however, inter-laboratory studies yielded unreproducible results and identified leakage issues with the test apparatus, and therefore the draft standard method (prEN13726- 5:2000) was not pursued.
In the absence of a published standard, SMTL have developed a bespoke test method to assess the bacterial barrier properties of wound dressings and other materials.
In this method, the test material is clamped between two flanged glass chambers, each filled with a liquid culture medium. A broth culture, containing a very small rod-shaped species of bacteria, is added to the fluid in one of the chambers and the apparatus incubated for a period of up to 7 days. During this time the culture medium is examined daily for evidence of bacterial transfer through the test material, as shown by turbidity of the liquid medium in the other chamber.
The test is usually run over a 7-day period, however this can be shortened or extended depending on the client's request.
The method has been refined over the 10 years since its initial conception, and the SMTL are UKAS accredited for the testing. The Chinese standard YY/T 0471.5 wet/wet method is essentially the same as the SMTL method.
Bacterial barrier testing is available on a commercial basis, however, organisations wishing to perform their own testing may also purchase the apparatus from SMTL.
If you have a product you wish to have tested or have any questions, please contact smtl.info@wales.nhs.uk
Relevant Standards
- YY/T 0471.5 Test Methods for Primary Wound Dressings; Bacterial Barrier Properties
Viral Barrier Testing
Viral barrier testing is performed in a similar way to the bacterial barrier, but a bacteriophage (virus that infects bacteria) is used as the inoculating organism. As the bacteriophage does not increase the turbidity of the broth, the broth is sampled and a plaque assay performed to detect the presence of bacteriophage which indicates passage of the phage through the sample.
Bacteriophage Φ-X174 is chosen because of its small size (0.027µm in diameter). The viral barrier testing can be performed on most flat surface materials.
If you have a product you wish to have tested or have any questions, please contact smtl.info@wales.nhs.uk