Abstract
On Buntings'' glycerol medium without phosphate, 1.0% casein hydrolysate possessed complete pigment inhibition activity against 12 strains of Serratia. The use of only 0.1% casein hydrolysate resulted in maximum growth and pigmentation. Of 20 individual amino acids, glutathione, niacin, thiamine, and NH4Cl (in 0.1 to 1.0% concns.), only glutamic acid suppressed pigment formation of all 12 strains. The pigment inhibition activity of glutamic acid but not of casein hydrolysate was neutralized by penicillin and bacitracin.