Sterile products are products which claim to be sterile or free of viable microorganisms. The main types of products claiming sterility are pharmaceuticals (e.g. injectables, nasal sprays, ophthalmics, etc.) and medical devices (e.g. titanium screws, other implantable devices, etc.) To confirm a claim of sterility for a product, Sterility Testing is required to determine if the products under the conditions of test are sterile as claimed.

A Sterility Test is designed to detect the presence of viable microorganisms that can potentially cause infection or other health-related issues. There are several compendial Sterility Test methods that can be used depending on product type (pharmaceutical or medical device): USP <71>, EP 2.6.1, JP and ANSI/AAMI/ISO 11737-2.

Sterility testing can be performed by two different methods: Membrane Filtration or Direct Immersion. Pharmaceutical products are typically tested by USP <71>, EP 2.6.1 and the recommended method is by membrane filtration unless the product is not filterable.  Medical device products are typically tested by ANSI/AAMI/ISO 11737-2 direct immersion method as most devices are solid and not filterable. Therefore, medical devices are immersed directly in broth.

Method 1:  Membrane Filtration

Using USP <71> as an example, the membrane filtration method involves filtering the required contents from a required number of containers and volumes as indicated in USP through a membrane filter of the proper type and a porosity of 0.45 µm. After filtration of the product, the filters are rinsed using either Fluid A, Fluid D or Fluid K. If microorganisms are present, these will be retained on the membrane filter. The membrane filters are then placed into two different nutritive broths that will support the growth of microorganisms if present: Tryptic Soy Broth (TSB) or Fluid Thioglycollate Medium (FTM).

TSB tests for aerobic microorganisms and FTM tests for anaerobic or microaerophilic microorganisms. Once the filtration process is complete, the TSB/sample mixture is incubated at 20-25oC for 14 days and the FTM/sample mixture is incubated at 30-35oC for 14 days. This can be performed by a closed system such as by SteritestTM or by filtering through a manifold and removing the filters and aseptically placing in the broths. The tests should be monitored daily or at regular intervals to look for the presence of growth or no growth.

If growth is obtained, the customer should be notified immediately. If the product renders the TSB or FTM turbid, then a transfer is made at 14 days to another container of the same medium. The original broths and the transfer broth are re-incubated for a minimum additional 4 days. If there is no growth at the end of the incubation period, the product complies with the test for sterility. If microorganism growth occurs, that means that the product in question does not meet sterility requirements and further investigation should be conducted.

Method 2:  Direct Immersion

The second type of methodology that can be used is referred to as Direct Immersion. This test is often performed for Medical devices e.g. titanium screws, IV tubing, needles and other solid products and pharmaceuticals that cannot be filtered due to the nature of the product. Since these specific types of products cannot pass through membrane filters, it’s necessary to instead put the samples directly into the required volume of growth medium (TSB and FTM).

The same procedure would follow as in membrane filtration testing in that the products are placed in incubators at the same temperatures for Membrane filtration for 14 days to determine if any microorganisms are present. If there is no growth at the end of the incubation period, the product complies with the test for sterility. If microorganism growth occurs, that means that the product in question does not meet sterility requirements.

Clean Room Testing Environment

The environment in which Sterility Tests are conducted can affect the overall outcome of the test itself. Therefore, these tests must be performed in a Clean Room that contains HEPA filtered air to preserve overall cleanliness, such as ISO Grade 6 Clean Room with testing conducted in a laminar flow hood with ISO Grade 5 classification. In addition to establishing room controls, those who perform the tests must wear sterile gowns and sterile gloves to keep the room conditions as aseptic as possible to prevent accidental contamination of the samples/broths when setting up the testing. Routine environmental monitoring (air and surface monitoring) of the room and personnel involved should be conducted during testing and on a routine on-going basis.

Sterility Test Method Suitability (Bacteriostasis/Fungistasis)

Sterility Test Method suitability (Bacteriostasis/Fungistasis) is required prior to routine testing of products for sterility. The suitability should be performed as you plan to test the samples either by membrane filtration or direct immersion using the required number of samples to be tested per batch and the volume of sample needed for each media (TSB and FTM). The procedure is conducted as per the test described previously but adding <100 CFU of the organisms specified in the compendia to the sample/plus media and control media without sample. The suitability broths are then incubated for not more than 5 days at the specified temperatures previously mentioned for each broth. If clearly visible growth of the microorganisms is obtained after the incubation, visually comparable to that in the control vessel without sample, either the product possesses no antimicrobial activity under the conditions of the test, or such activity is satisfactorily eliminated. The routine Sterility Testing is then conducted based on the suitability and is not changed unless the method or product formulation changes.

At CPT, we have everything needed to not only carry out Sterility Testing, but execute it to the highest standard. We perform both membrane filtration and direct immersion for pharmaceuticals and medical devices in our sterility clean room with aseptic conditions, HEPA filtration and our gowning system. Depending on the method required for your product, we can perform Sterility Testing by USP <71>, EP 2.6.1, JP and ANSI/AAMI/ISO 11737-2 compendial standards.

Why Choose CPT for your Sterility Testing?

When it comes to Sterility Testing of any type, CPT can address your testing needs.  Our team of expert chemists and microbiologists can provide accurate testing, whether it be routine monitoring or testing support of validation activities.  Consulting services are also available to assist you in identifying problems within your water purification system.  Whatever your water testing needs, CPT is ready to lend assistance.

Think of CPT as an extension of your Quality Team. Accurate testing conducted within a highly compliant testing environment. Contact us at your earliest convenience.

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