The Synthesis of p-Aminobenzoic Acid and Folic Acid by Staphylococci Sensitive and Resistant to Sulphonamides

Abstract

The synthesis of p-aminobenzoic acid and folic acid was investigated in three strains of Staphylococcus sensitive to sulfonamide drugs, and in four substrains resistant to sulfonamides. Another strain (S. aureus R 122) which was resistant to sulfonamides when isolated was also examined. A microbiological assay was used to measure the synthesis of p-aminobenzoic acid during the growth of organisms in a partially defined medium. S. aureus R-122 formed about twenty times as much p-aminobenzoic acid as did any of the other strains, among which the synthesis showed only small variations and was not greatly affected by growth of the organisms in presence of sulfathiazole. Folic acid was assayed as Lactobacillus casei factor. The response curve of the assay organism to extracts of every strain of Staphylococcus examined was the same; but it differed from the response to known forms of folic acid. The active material had little growth-promoting activity for Leuconostoc citrovorum or for Streptococcus faecalis. Washed suspensions of S. lactis 2102 R formed about 10 times as much folic acid as the sensitive parent strain (2102) from glucose, p-aminobenzoate and glutamate; the sulfonamide -resistant substrain (2102-R) also formed more folic acid during growth. However, a second resistant S. lactis substrain (2102-R 2) formed little more folic acid than did the parent strain. S. aureus R-122 synthesized an amount of folic acid similar to that formed by S. lactis 2102-R. With two other strains (S. aureus H and JHM) the synthesis of folic acid was not increased when resistance was acquired. Washed suspensions of all the sulfonamide resistant substrains were able to synthesize folic acid in the presence of higher concentrations of sulfathiazole than were the sensitive strains.