Bacterial Plates - (Jul/19/2007 )
How long the bacterial colonies are alive on the LB media.
Consensus is that if you seal a plate with parafilm and keep it at 4C, it can be used up to a month.
Bacteria colonies may not be as good that long. I would suggest streak onto other plates after 1 week at the latest.
It also depends greatly on the species of bacterium, the media and the thickness of the plates. E. coli will last for a month. Others will be longer, and others again will be shorter.
If you've already waited a long time, and you're asking because you want to know if they're still alive... Well, just subculture them and check
If you haven't yet stored them for a long time, then just subculture them weekly and you won't have to worry.