Luria Agar (Millers Modification) is based on LB Medium according to Miller's descrption. Its modification consists of a minimal concentration of sodium chloride. This medium is used for the growth and maintenance of E. coli strains used in molecular microbiology procedures. It is used for strains in which the optimal concentration of salt is 0,5 g/l. These strains are generally derived from E. coli K12, which are unable to produce vitamin B, so this media is formulated to enhance the growth of nutritionally demanding microorganisms. This strain of E. coli has been further modified through specific mutation to create an auxotrophic strain that is not capable of growth on nutritionally deficient media. Some plasmid vectors replicate to high copy numbers and do not require selective amplification. Some vectors do not replicate so freely and need to be selectively amplified. Antibiotics may be added to inhibit host synthesis and, as a result, prevent replication of the bacterial chromosomome. Tryptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is source of vitamins, particularly the B-group. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Bacteriological agar is the solidifying agent. Luria Agar (Miller's Modification) has a different sodium chloride level than other media such as LB Agar (Lennox) (Cat. 1083) or Luria Agar (Miller's LB Agar) (Cat. 1552). This allows to select the optimum salt concentration of the medium for a specific strain.
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