The synthesis of p-aminobenzoic acid and folic acid by staphylococci sensitive and resistant to sulphonamides.

Abstract

SUMMARY The synthesis of p-aminobenzoic acid and folic acid was investigated in three strains of Staphylococcus sensitive to sulphonamide drugs, and in four substrains resistant to sulphonamides. Another strain (Staphylococcus aureus r122) which was resistant to sulphonamides 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 r122 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 sulphathiazole. 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 citroυorum or for Streptococcus faecalis. Washed suspensions of Staphylococcus lactis 2102r formed about 10 times as much folic acid as the sensitive parent strain (2102) from glucose, p-aminobenzoate and glutamate; the sulphonamide-resistant substrain (2102r) also formed more folic acid during growth. However, a second resistant S. lactis substrain (2102r2) formed little more folic acid than did the parent strain. S. aureus r122 synthesized an amount of folic acid similar to that formed by S. lactis 2102r. 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 sulphonamide resistant substrains were able to synthesize folic acid in the presence of higher concentrations of sulphathiazole than were the sensitive strains.