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[itried]

I'd like to culture some soil this week for lab, but all I have is very old trypticase soy agar whose packaging says, "Use by November 7, 2008." It's all dried up in the Petri dish; can I revive it by adding water? I just added some water and within minutes it smelled funky like fresh agar. I only want to culture field soil for use in a classroom activity -- I'm not trying to win a Nobel Prize or anything.

[pollinate]

If that's the only option (vs. no cultures for lab) then go for it.  What's the worse that can happen - you have some additional microbes?  Or maybe not so much grows as usual?

Heck, it may turn out to be the perfect medium for some previously unculturable stuff!

[itried]

Thanks for the encouragement pollinate! I'm willing to try it myself to see what happens, but ideally I'd like to have students search out and collect the soils they want to culture, which they love doing; I don't want to get them excited about the activity if the agar is totally defunct.

[chaosbydesign]

I have successfully revived and cultured bacterial strains from dried up agar plates before, but never tried to reuse the agar. I am not sure that it would work all that well.
 
I'm not sure from your post what you actually have -- do you have already-poured plates of TSA that have dried out? Does anyone in other labs have tryptone, soytone and plain agar?

[itried]

Good question chaosbydesign. I have pre-poured TSA plates that haven't been used -- they're just old and dried up. Have you had success with dried-up, unused plates that you revived by moistening? I don't have access to any other agar here -- this is all I have.

[chaosbydesign]

Have you had success with dried-up, unused plates that you revived by moistening?

No, I've just managed to save bacteria from them. I have never tried to used old dried up agar. I have used out of date ingredients in LB broth before, though, and that was fine.

I am wondering if the drying out will have affected the nutrients in the agar. I know for sure that you're not supposed to re-autoclave media (though people do it) so I am pretty sure that reconstituting and reautoclaving dried up agar is not the best thing in the world. However, if you're just looking for something to grow and aren't all that concerned about the results, then you might be OK doing it.

[itried]

Thank you for your thoughts. I'm going to try it -- I'll write again in a week or so to let you know what happens!

[itried]

... okay, I just prepared a plate. Grow, grow ...