SUMMARY: The nutritional requirements of eight strains of type A were studied. Five strains required for optimum growth the three vitamins, biotin, thiamine and -aminobenzoic acid, one strain showed additional demands for nicotinic acid and pyridoxin, whilst two non-toxigenic strains required biotin and -aminobenzoic acid. Biotin could be replaced by oleic acid and a number of Tweens, -aminobenzoic by folic acid, citrovorum factor or a mixture of thymine and purines.

All the strains tested showed good growth in a medium containing at least 2.5% casein hydrolysate (Difco), equivalent to about 0.18% N. The casein hydrolysate could be replaced by a mixture of amino acids, of which the following nine were essential: tryptophan, threonine, valine, leucine, isoleucine, methionine, arginine, phenylalanine and tyrosine. The last three acids were required in unusually large amounts. Growth in chemically define medium was followed by a rapid lysis. In spite of optimum growth, the toxin titre in the defined medium was about 50,000 LD doses/ml., i.e. approximately ten times less than that obtained in complex media.


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