Inhibitory Effect of Saliva on Glutamic Acid Accumulation by Lactobacillus acidophilus and the Role of the Lactoperoxidase-Thiocyanate System

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Abstract
Clem , W. H. (University of Washington, Seattle), and S. J. Klebanoff . Inhibitory effect of saliva on glutamic acid accumulation by Lactobacillus acidophilus and the role of the lactoperoxidase-thiocyanate system. J. Bacteriol. 91: 1848–1853. 1966.—Saliva contains an antimicrobial system which inhibits the growth of Lactobacillus acidophilus , as well as a number of other organisms, in complete growth medium. This antimicrobial system consists of the salivary peroxidase (lactoperoxidase) and thiocyanate ions, and requires the presence of H 2 O 2 . Saliva inhibits the accumulation of glutamic acid and certain other amino acids by resting cells. This effect of saliva is decreased by dialysis, and thiocyanate ions restore the inhibitory effect of dialyzed saliva. The inhibitory effect of saliva is decreased by heat (100 C, 10 min), and lactoperoxidase restores the inhibitory effect of heated saliva. Thus, the inhibition of glutamic acid accumulation by saliva appears to be due in part to the lactoperoxidase-thiocyanate antimicrobial system. H 2 O 2 increases the inhibitory effect of both saliva and the lactoperoxidase-thiocyanate system on glutamic acid accumulation. The inhibition of glutamic acid accumulation is not preceded by a loss in microbial viability. The glutamic acid accumulated by L. acidophilus under the conditions employed remains largely (over 90%) as free glutamic acid. This suggests that saliva and the lactoperoxidase-thiocyanate-H 2 O 2 system inhibit the net transport of glutamic acid into the cell.