Media assays are substances in liquid, semi-solid or solid form, containing natural or synthetic components, used to ensure the proliferation or maintain the viability of microorganisms. The preparation and use of media for testing is an important part of microbiology laboratory testing. The quality of the medium test itself, whether it is properly preserved, whether it is correctly prepared and used, all directly affect the accuracy of the test results.

Purchase and acceptance of culture medium testing

 1. Buy

From the perspective of the quality of the culture medium test itself, there are differences between products from different manufacturers, or even different batches of products from the same manufacturer. According to ISO/IEC17025 "General Requirements for the Capability of Testing and Calibration Laboratories", selecting qualified suppliers after evaluating media suppliers is an important step in the media procurement process. Enterprises with high reputation in the product market, strong quality assurance ability and service assurance ability should be selected; whether the enterprise has passed the quality management system certification is a relatively objective evaluation index. The manufacturer needs to provide: the name of the detected components of the culture medium and product number, batch number, pH value before use, storage information and expiration date, performance evaluation and test strains used, technical data list, quality control certificate, necessary safety/hazard data and other information.

2. Acceptance

After the purchased medium arrives, a special person should be assigned to do the acceptance work, and the information provided by the manufacturer, medium name, specification quantity, appearance characteristics, batch number, etc. should be carefully checked, and the shelf life meets the requirements. After the arrival of each batch of culture medium, the quality inspection of the culture medium should be carried out, and it can only be put into use after meeting the requirements specified in the detection method.

Media Storage 

Dry powder media should be stored in a cool, dry place out of direct sunlight; unopened media assays can be stored at room temperature for up to  2 years. After opening the bottle, the dry powder medium is easy to absorb moisture. run out. Routine inspections of storage media should be carried out on a regular basis, such as re-checking of container tightness, date of first opening, sensory inspection of contents, and should not be reused if the media shows agglomeration, abnormal color and other signs of deterioration.  

Preparation of medium assay

1. Reclaimed water

Distilled water or water of equivalent quality with a resistivity not lower than 300,000Ωcm should be used for the preparation of the culture medium, and deionized water produced by an ion exchanger should not be used.

2. Weigh

Use a special corner scoop when weighing to avoid cross-contamination affecting the test results; dry powder medium is easy to absorb moisture, if possible, try to weigh in a room with low humidity.

3. Rehydration 

Do not use copper or iron pots when rehydrating, so as not to mix ions into the culture medium and affect the growth of microorganisms; the size of the container should be more than twice the total volume of the culture medium after rehydration, so as not to be heated and dissolved during the cultivation process. The base overflows; the medium containing agar powder can be soaked for a few minutes before heating to dissolve; be sure to stir when heating the medium, especially the agar medium. To avoid burning and boiling, it is best to use a boiling water bath for small amounts of media assays. Nutrients in the combustion medium are destroyed and toxic substances are produced. If coking is found, or the medium is not uniformly dissolved and overflows, the medium cannot be used and should be re-prepared. When testing the remelted agar-based medium, it should be heated in a boiling water bath or flowing steam, and it can only be heated twice at most, and the unused medium should be discarded after the second remelting.