Preparation, Storage, and Contamination Control of DMEM Medium: A Beginner's Guide to Animal Experimentation

Two common forms: dry powder and liquid

DMEM medium usually exists in laboratories in dry powder or liquid form. The dry powder type has a relatively long shelf life and is convenient to transport, but it needs to be prepared, filter-sterilized, and supplemented with a certain amount of sterile water by the user. The liquid type, or ready-to-use type, is convenient to use; after opening, it can be stored according to the recommended conditions, making it suitable for beginners who have just started animal cell culture. Regardless of the form, before use, the instructions and label should first be checked to confirm whether it contains components such as phenol red, glutamine, and sodium pyruvate, so as to avoid conflicts with existing protocols. The general requirement is: the water used to prepare dry powder should meet cell culture grade standards, and tap water or ordinary mineral water must not be used directly.

Preparation steps and pH adjustment

If dry powder DMEM is chosen, during preparation the dry powder should first be poured into an appropriate amount of culture-grade purified water and stirred until fully dissolved. Many formulations require the addition of a certain amount of sodium bicarbonate to adjust buffering capacity. After dissolution, the liquid needs to be brought up to the target volume, then tested with a pH meter or precision pH paper. The pH of common DMEM is generally adjusted to around 7.2 to 7.4. During adjustment, sterilized acid or base solutions can be added slowly while stirring to avoid local over-acidification or over-alkalinization. After preparation is complete, it usually needs to be filter-sterilized through a membrane with a pore size of 0.22 micrometers or smaller. The entire operation is best performed in a biosafety cabinet or clean bench to reduce the risk of microbial contamination.

Storage conditions and shelf-life management

Liquid DMEM medium is generally recommended to be stored protected from light at 2 to 8 degrees Celsius. Too low a temperature may cause the liquid to freeze or components to precipitate, while too high a temperature may accelerate the degradation of certain components. Before each use, the color can be observed: DMEM containing phenol red is usually red or orange-red at normal pH. If the color is obviously purplish or yellowish, it may be related to alkaline changes or microbial metabolism. After opening, the medium should not be left at room temperature repeatedly for long periods; after use, it should be returned to refrigeration promptly. Laboratories can establish simple shelf-life records, including the opening date, lot number, and user. Even if the use remains unchanged, it is not recommended to continue using it beyond the storage period recommended in the product instructions.

Keep contamination out of the culture flask

In animal cell culture, bacterial and fungal contamination are common problems. Although DMEM medium has undergone sterilization treatment, contamination may still be introduced during use by handling. First, before operation, the biosafety cabinet ventilation should be turned on, and the work surface and the outer walls of reagent bottles should be wiped with a suitable disinfectant. When aspirating liquid, disposable sterile pipettes or sterilized tips should be used, and mouth pipetting or the use of non-sterilized tools should be avoided. The time the bottle mouth is open should be shortened as much as possible, and the same pipette should not be used across different reagent bottles. If the medium is found to be turbid, contain flocs, or have an odor, do not continue to use it. Regularly cleaning the incubator, water pan, and operating area helps reduce the overall probability of contamination. Good preparation and storage habits are the foundation for stable animal experimental data.