Studies on the Amino Acid Decarboxylases of Oral Lactobacilli

¹ Department of Bacteriology and Immunology, School of Medicine, University of North Carolina, Chapel Hill

The optimum conditions for the production of amino acid decarboxylases by oral lactobacilli were determined. They included incubation at 37° C., harvesting when the point of maximum acid production was reached, and growth in a medium composed of 0.5 per cent Bacto-yeast extract, 2 per cent glucose, and 1 per cent powdered casein (acid-hydrolyzed, vitamin- and salt-free). Using these conditions, 58 strains of oral lactobacilli were tested manometrically for the presence of four amino acid decarboxylases. Glutamic acid decarboxylase was the most frequently occurring decarboxylase, followed by histidine and, finally, lysine decarboxylases. Sixty-seven per cent of the organisms produced carbon dioxide from arginine, and it was concluded that arginine decarboxylase was not involved but that the carbon dioxide production resulted from the action of arginine desimidase and citrullinase.