Growth Requirements of Streptococcus mitis and Sulfonamide Resistance.

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Abstract
The vit. requirements of 3 strains of S. mitis, one S. fecalis, and one strain of a trained sulfathiazole-resistant S. mitis were compared. The S. mitis strains would not grow in the absence of Ca pantothenate or nicotinic acid, and growth was stimulated by riboflavin, p-aminobenzoic acid (PAB), pyridoxine, and biotin. Two strains were stimulated by thiamine. Pteroylglutamic acid (PGA) was not required. The resistant variant showed the same growth response to all the vits. as did the strain of S. fecalis. Little or no growth was observed in the absence of Ca pantothenate and PGA. Nicotinic acid, pyridoxine, and biotin stimulated growth, while the absence of thiamine, riboflavin, and PAB had no appreciable effect. The most significant difference between the S. mitis strains and the resistant variant seemed to be the requirement for PGA shown by the resistant strain. Four additional S. mitis strains were found to grow completely in the absence of PGA, while their resistant variants showed no growth. The acquired resistance may be due to the variant using preformed PGA rather than depending upon the synthesis which is inhibited by sulfathiazole.