In the field of microbial testing, culture media serve as the "soil" for cultivating microorganisms, and their storage conditions and methods are directly related to the accuracy and reliability of test results. Particularly in food and environmental sampling tests, correct preservation of culture medium is crucial for target microorganisms like Escherichia coli, coliforms, and Staphylococcus aureus. This article will delve into the key points and considerations for the preservation of culture medium to ensure the smooth progress of testing work.
Upon the arrival of purchased culture media, microbial testing personnel must immediately carry out a stringent acceptance process. This includes verifying whether the composition and added quantities of the culture media meet standard requirements and confirming that its intended use matches experimental needs. Additionally, check if the culture media’s expiration date is sufficient, if the packaging is undamaged, and whether the necessary quality control reports are included. These steps are fundamental to ensuring the culture media’s quality is up to standard and meets experimental needs.
The storage environment's temperature, humidity, and light exposure are core factors affecting the shelf life of culture media. Unopened culture media should be stored strictly according to the conditions indicated on its packaging, avoiding high temperatures, humidity, and direct sunlight. Once opened, immediately record the first opening date and closely monitor the physical state of the media during subsequent storage, such as whether the powder clumps up or its color appears abnormal, to assess its quality status. If any signs of moisture-induced clumping or obvious physical changes are observed, discontinue use immediately to prevent compromising test results.
For prepared plates, tubes, or bottled culture media, managing their shelf life is equally important. Once sterilized culture media is opened for use, the remaining portion is generally not recommended for reuse to avoid external contamination. Unused agar media is only allowed to melt once, as repeated melting can destroy its nutrients. Additionally, sterilized media should be promptly removed from the autoclave to prevent prolonged exposure that could lead to quality degradation. According to standards like GB 4789.28-2013, culture media generally need to be stored in a cool, dry place away from light, at 2℃-8℃, with clear labeling of the culture media’s name, preparation date, and expiration date. For media containing unstable additives or active chemicals, it is essential to adhere to the principle of preparing and using immediately.
If solid culture media need to be re-melted after sterilization, it should be done in a heated water bath, induction cooker, or electric heating jacket, and it is only permitted to melt once. The melted media should be kept in a water bath at 45℃-50℃ and used as soon as possible to maintain its optimal state. Although this step might seem minor, it directly affects the uniformity of the media and the growth condition of microorganisms.
During the use and preservation of culture medium, situations such as microbial growth or exceeding the expiration date are inevitable. When this occurs, the disposal method should be safe, environmentally friendly, and in compliance with legal regulations. It is generally recommended to use a high-temperature, high-pressure method at 121℃ for 30 minutes to ensure that microorganisms in the media are fully eradicated, preventing environmental contamination.
In summary, the considerations and preservation of culture medium involve multiple aspects, from acceptance, storage, and shelf life management to re-melting, temperature maintenance, and final disposal. Each step must strictly adhere to relevant standards and guidelines. Only by doing so can the stability and reliability of culture media be ensured, providing strong support for food and environmental sampling tests.
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