Part of Thermo Fisher Scientific
USER-LABORATORY QUALITY CONTROL TESTS ON PREPARED MEDIA
Quality control tests should be carried out by the end-user laboratory to ensure
that the performance characteristics of the medium are within specification
and that the methodology of medium preparation is satisfactory.
Each lot/batch of prepared medium should be subjected to a minimal testing programme which will ensure that it is acceptable and will demonstrate a typical bacterial performance.
1 pH value: check that the pH of the prepared medium, when tested in final form at ambient temperature (25°C) lies within the range given on the product label. The medium should be discarded if the pH value lies outside the specified range.
2 Sterility: a representative sample of each lot/batch of medium should be incubated for 2-5 days at 35-37°C. As a general rule, for a lot of 100 or less units a 3-5% sample should be tested. For a larger lot, 10 random plates or tubes are taken. There should be no evidence of microbial growth after incubation. Discard all sterility samples when the tests have been completed.
3 Growth performance: test the growth support properties of the product by inoculating the medium with appropriate stock cultures and/or fresh isolates. Use a standard inoculation procedure and examine the quantitative and qualitative results obtained. If testing new lots/batches of media, inoculate old and new lots in one test and compare the performance of the two lots side by side.
4 Stability: periodically perform the above procedures on stored prepared media in order to determine whether the storage conditions will give optimal results.
NOTE: If a medium does not perform to expectations and all the manufacturer's recommendations have been followed, then the following steps should be taken:
1 Record the nature of the problem and the method of
preparation of the medium.
2 Note the lot/batch number and the date it was received.
3 Call the Technical
Support department of the company.