Amino acid decarboxylases of lactic acid bacteria.

Many strains of a wide variety of bacterial species have been studied for their amino acid decarboxylase activity (Gale, 1946). However, to our knowledge the lactobacilli have not been examined. It has been shown in our laboratory that oral lactobacilli may be classified into three types according to their ability to attack certain carbohydrates, intensity of acid production from glucose, and by their dehydrogenase activity (Clapper and Heatherman, 1949). One of these groups appears to be more closely associated with dental caries than the other two. It occurred to us that a study of another biochemical property, the amino acid decarboxylase activity, of these organisms might add additional information for determining the validity of the classification into the three types. Furthermore, since decarboxylase activity may determine the pH of the organism's environment, it was thought that such a study might indicate why one group could be more capable of initiating a carious lesion than another. We also have included a study of the amino acid decarboxylase activity of some parent strains of Streptococcus mitis and their sulfathiazole-resistant trained strains. The resistant strains have been found to exhibit many of the properties of enterococci (Clapper and Heatherman, 1950). Gale (1940a) has shown Streptococcus faecalis to possess tyrosine decarboxylase but no other amino acid decarboxylase. He has shown that this organism produces CO2 from arginine by a "dihydrolase" (Gale, 1940b). It seemed of interest to determine whether the trained resistant strains resembled S. faecalis in these properties as well as those previously reported.