In the laboratory, we usually store E. coli in two ways.
1) For short term storage (a month or less), we simply put E. coli at 4 degrees Celsius (in the refrigerator).
This includes E. coli cultures grown both in a broth and on an agar plate. Note that if you have E. coli on an agar plate, it is best to seal edges of the agar plate so that it does not dry out over time.
2) The second way we store E. coli is at -80 degrees Celsius.
This storage requires that the E. coli be frozen in a special solution containing the chemical glycerol. I don’t know the exact length that you can store E. coli at -80, but I seem to remember that such stocks can still produce viable E. coli _at least_ a year later. For most purposes, however, short term storage is easy and sufficient.
Just be careful not to store the bacteria in a place where you also store food and beverages!
We have special refrigerators used only for bacteria, so that you never risk contaminating food with your E. coli. Good luck! ETC