Variations in the metal content of some commercial media and their effect on microbial growth

The cation content in commercial media obtained from two manufacturers showed considerable variation. Even different batches of the same make were found to be inconsistent in the content of metal ions. With cultures of Cytophaga sp. and Yersinia pseudotuberculosis in base media, growth stimulation was dependent on additions of certain commercial media. It could be demonstrated that this stimulation was derived solely from increased Mg(2+) concentration in the media.