Can DMEM still be used if there is a small amount of flocculent material after two weeks of high sugar bottle opening?

For future large-volume arrivals, first aliquot on the clean bench to reduce repeated opening of the main bottle and temperature fluctuations. Store at 4°C protected from light, and do not place it too close to the back wall of the refrigerator to prevent localized freezing or uneven temperature. Do not pour DMSO/serum, etc., directly back into the bottle. Keep the bottle opening sterile when opening; before use, warm to room temperature and swirl gently, do not shake vigorously. Repeatedly opening high-glucose DMEM outside a CO2 environment will cause pH changes that promote precipitation. If laboratory usage is high, you can take a one-week supply to the cell culture room each time and store the rest in the reagent storage room.

If this group insists on saving, it is recommended to only conduct non critical experiments. Do not take the bottom of the supernatant. After filtering at 0.22 µ m, add a small amount of serum and antibiotics. Set up a blank well with only culture medium and observe in the incubator for 3-5 days. Then inoculate 2-3 passages of test cells to observe adhesion and proliferation. Any color that becomes dull, has an odor, or experiences a rapid decrease in pH should be immediately discarded. Instead of continuing to struggle, it's better to open a new bottle with a new batch number for formal experiments and contact the supplier at the same time. The cost of experimental failure caused by problems with the culture medium is usually much higher than the price of a bottle.

Exchange depends on the situation. Please record the bottle opening date, storage temperature, photos of the flocculent material, and batch number, and contact the dealer's technical support. Generally, if sedimentation occurs after opening the bottle of liquid culture medium, the supplier may not consider it a quality issue and will first let you make your own judgment or return it for testing. If there are still unopened bottles in the same batch, there is even more reason to request a replacement or exchange. Suggest placing one unopened bottle from the same batch at 4 ° C for observation and taking photos as evidence. Do not open it first, otherwise it will be more difficult to define responsibility. It would be better to obtain COA and transportation temperature records.

White fine flocculent material, non-turbid color, odorless—in most cases this is phosphate/carbonate precipitation or protein precipitation, not mycoplasma—mycoplasma does not produce visible flocculent material. However, this cannot completely rule out contamination, especially slowly growing fungi. The safe approach is: do not use this bottle for precious or experiment-critical cells. You can take the supernatant, centrifuge it, filter it through 0.22 µm, inoculate the filtered solution into blank wells or test cells, observe for 3-5 days, and then perform mycoplasma testing. If it is only precipitation, gently shaking in a 37°C water bath may sometimes dissolve it, but do not directly continue using the original solution.