For propogation, cultivation and maintaince of E.coli mutant used in microbiological assay of Vitamin B12. B12 Culture Agar (E.coli Mutant Culture Agar) is recommended for cultivation and maintenance of E.COLI ATCC 11105. Medium contains Casein enzymic hydrolysate which helps to provide provides nitrogen and amino acids for the growth. Yeast extract is vitamin source in the medium while sucrose is carbon and energy source. Potassium salt provides buffering capacity to the medium and sodium, magnesium and ferrous salts control permeability of bacterial cells. Liver extract enriches the medium for growth of E. COLI as well as inhibits gram positive bacteria.