Utilization of Pteroylglutamic Acid Antagonists for Growth by a Strain of Streptococcus faecalis ∗

Summary

I. S. faecalis/A, an organism made resistant to amethopterin, grew well on a series of PGA antagonists except those with a methyl group in the 9 position. 2. This culture was also more efficient than the parent strain of S. faecalis in the utilization of PGA analogs that served as growth factors for both organisms, with the notable exception of CF. The amount of CF (leucovorin) required for HMG was approximately the same for each strain. 3. Aminopterin was as effective as PGA in reversing the toxicity of aninopterin and adenopterin in the growth of 5. faecalis/A.