Oiginally developed by Bertani, this media is a very common and nutritionally rich growth media for E. coli. This media is extensively used for the maintenance and propagation of plasmid DNA and for the growth of the recombinant strains which contain protein expression vector. The ingredients provide all the growth factors required for the E. coli strains. Top agar is used to distribute bacteriophage and bacterial cells uniformly on the thin layer over the surface of a plate. Top agar contains less amount of agar (0.7%) than usual plates and so stays in a molten state for several days when it is kept at 45° to 50°C.