Resistance to Folic Acid Analogues in a Strain of Streptococcus faecalis.

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Abstract
Bioautographs of paper chromatograms of several 4-amino analogs of folic acid indicate the presence of inhibitory and growth-promoting contaminants. All the antagonists studied contained sufficient pteroylglutamic acid (PGA) or pteroic acid to account for their apparent utilization for growth by an antagonist-resistant strain of S. faecalis. The resistant strain had a lower requirement for PGA and pteroic acid and a much greater capacity to convert PGA to citrovorum factor than did the parent antagonist-sensitive strain. Significant inhibition of the formation of citrovorum factor from PGA by resting cells of the resistent organism occurred only with very high concns. of aminopterin or amethopterin.