Inhibition of Saccharomyces cerevisiae by p-aminobenzoic acid and its reversal by the aromatic amino acids.

It has been known for many years that p-aminobenzoic acid at high concentration is inhibitory to a variety of organisms, including rickettsiae (I), bacteria (2, 3), fungi (4), protozoa (5), and plants (6). The site of inhibition by p-aminobenzoic acid in most of these organisms has not been established. However, Davis (3) has shown that the bacteriostatic activity of p-aminobenzoic acid toward Escherichia coli (strain W) is reversed competitively by p-hydroxybenzoic acid. The inhibition was reversed also to a limited extent by shikimic acid and by 5-dehydroshikimic acid. Reversal by p-hydroxybenzoic acid of the rickettsiostatic action of p-aminobenzoic acid has been reported (7,8). The present communication wll report that the aromatic amino acids, but not p-hydroxybenzoic acid or shikimic acid, exert a reversing effect on inhibition of Saccharomyces cerevisiae by p-aminobenzoic acid, and that shikimic acid accumulates in the culture medium in the presence of p-aminobenzoic acid.