The Growth and Toxin Production of Corynebacterium Diphtheriae in Synthetic Mediums

The synthetic medium devised by Braun and Ilofmeier was found to afford a better basic medium for the study of growth and toxin production of C. diphtheriate than the mediums of Uschinsky, Hadley or Dolloff. The comparative nutritive values of ten amino-acids were studied, three strains of Park 8 and three more recently isolated strains being employed. The simple mono-amino-acids, such as alanine, phenylalanine, valin and especially glycine, were more effective in stimulating growth in a synthetic medium than the more complex mono-amino-acids that were tried. The nitrogen-bearing constituents o f the Braun and Ho f meier medium were modified considerably before moderate production of toxin was obtained. The cystine content was increased fourfold, to the point of maximum solubility in this solution, asparagin or ammonium succinate replaced the sodium aspartate, and glycine was added. A virulent strain, 4703, one strain of Park 8, and an avirulent strain, 4104, were adapted to growth on synthetic mediums. The virulent strain 4703S produced toxin on synthetic mediums after six months' cultivation on protein-free mediums. The most potent toxin produced by strain 4703S had a minimal lethal dose of 0.1 cc. and a skin test dose of 0.0001 cc. Strain Park 8T elaborated a weaker toxin in synthetic mediums, with a minimal lethal dose of 0.5 cc. and a skin test dose of 0.0005 cc. The experiments described seem to indicate that several factors control the production of toxin in synthetic mediums. It appears that the strain must be thoroughly adapted to rapid growth and formation of pellicle in protein-free medium. It appears, further, that the medium must provide not only nutrients for growth and pellicle formation, but these nutrients should also favor the appearance or maintenance of the toxigenic variants that occur in consequence of a dissociative process.