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How do I store non-sterile culture media in dissolved form in the fridge in a clean but non-sterile container?

The powder of the media (Broth, Nutrient agar, MAC, or MH agar) will be put in a glass bottle filled with distilled water and then dissolved/mixed in the microwave.

Would a 12-hour to 16-hour storage in the fridge prior to sterilization, thereafter, affect the media performance?

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2 Answers 2

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So long as you are careful in making this, so as to not add gross+ contamination (hair, don't put your fingers in it, etc.) and use clean glassware, then a storage at 4 C will inhibit almost all bacterial growth from almost all common species, and those that are capable of growing at 4 C tend to grow very slowly.

You don't need to microwave before sterilization generally - the autoclave will melt the agar much better than you can do in the microwave and is easily mixed in by a swirl of the bottle after removing from the autoclave.

+ This means bulky or heavily, not "ewww disgusting". See definition 4: https://www.merriam-webster.com/dictionary/gross

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  • $\begingroup$ I'm melting to mix. Do you mean that i generally don't need to mix prior to autoclave, just add powder + water, then autoclave and swirl after its out? $\endgroup$ Oct 24, 2023 at 4:55
  • $\begingroup$ @FreezingSoul you should dissolve liquid media in cold water, then autoclave. Media with agar, you should dissolve the soluble components in cold water add the agar (if separate), then autoclave. No need for microwave to dissolve the agar. $\endgroup$
    – bob1
    Oct 24, 2023 at 7:19
  • $\begingroup$ I meant to ask, generally, is there no need to mix prior to autoclaving? I think i had pimpled MacConkey agar when i didn't boil it prior to autoclaving. $\endgroup$ Oct 24, 2023 at 12:19
  • $\begingroup$ I didn't swirl, to be honest after receiving my autoclaved media, but it was clear. $\endgroup$ Oct 24, 2023 at 12:32
  • $\begingroup$ @FreezingSoul I usually keep a magnetic stir bar in the flask when autoclaving media. Makes it easy to mix while cooling, which is especially important when I have to add heat-sensitive amendments (like vitamins or certain amino acids). I honestly wonder why every SOP ever tells us to dissolve agar with heat before autoclaving, since every lab person I know just mixes it in cold and lets the autoclave do the heating/dissolving. $\endgroup$
    – MikeyC
    Nov 7, 2023 at 16:58
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Media performance in terms of what? What are the temperatures in the fridge? Assuming you are storing sterile media, refrigeration will not affect anything. What might be affected is the media and culture. Your question sounds like you are storing media without cells, and nothing will be affected.

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  • $\begingroup$ "Non sterile", not "sterile" $\endgroup$ Nov 9, 2023 at 1:26

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