A stasis test, also known as an inhibition test, checks if a product contains substances that prevent microbial growth, ensuring the sterility test remains valid. Essentially, it verifies that the test environment can still support microbial growth at the end of the sterility test incubation period.
Purpose of a Stasis Test
The primary goal of a stasis test is to confirm that no inhibitory substances are present in the tested product that could falsely indicate sterility. This is crucial because:
- Ensuring accurate sterility testing: It guarantees that the culture media used in sterility testing remains capable of supporting microbial growth throughout the incubation period.
- Detecting inhibitory substances: It identifies any compounds in the product that might suppress or inhibit the growth of microorganisms. According to the reference (5.6), a stasis test, or inhibition test, is performed to ensure that no inhibitory substances remain in the product and that the media is still capable of supporting the growth of micro-organisms at the end of the sterility test incubation period.
- Validating sterility results: It ensures that a negative sterility test result accurately reflects the absence of viable microorganisms, rather than a false negative due to inhibition.
How a Stasis Test Works
While the reference doesn't detail the exact procedure, a general understanding can be provided from common industry practices:
- Inoculation: A small number of microorganisms (typically specified strains relevant to sterility testing) are introduced into the test sample (product).
- Incubation: The inoculated sample is incubated under the same conditions as the sterility test.
- Observation: After the incubation period, the growth (or lack thereof) of the microorganisms is observed.
- Comparison: The growth in the test sample is compared to the growth in a control sample (without the product) to assess any inhibitory effects.
Interpretation of Results
- Growth comparable to the control: This indicates that the product does not contain inhibitory substances and the sterility test results are valid.
- No growth or significantly reduced growth compared to the control: This suggests the presence of inhibitory substances, potentially invalidating the original sterility test and requiring further investigation.
