Differences in the synthesis of folic acid and 5-amino-4-imidazolecarboxamide in sulfathiazole sensitive and resistant strains of Escherichia coli.

Several studies have been reported on the relation of sulfonamide resistance to folic acid synthesis. Miller (Proc. Soc. Exptl. Biol. Med., 57, 151, 1944) reported that a decreased amount of folic acid was produced in cultures containing sulfanilamide by both sensitive and resistant strains of Escherichia coli, and Harrison and Clapper (Bacteriol. Proc., 1950, 39) reported loss of the ability to synthesize folic acid by sulfonamide resistant Streptococcus mitis. Lascelles and Woods (Brit. J. Exptl. Pathol., 33, 288, 1952) indicated increased synthesis of folic acid by a sulfathiazole resistant strain of Staphylococcus aureus. Our unpublished data obtained under the conditions described here with our Staphylococcus aureus strain 3A, sensitive and resistant to 3,000 ,ug ST/ml, did not show any difference in the amounts of folic acid synthesized. The present note deals with the relation of growth, folic acid production, and accumulation of 5-amino-4imidazolecarboxamide and its riboside (AIC) in various strains of E. coli. Growth was measured turbidimetrically, and the dry weights of cells were calculated by means of a turbidity versus dry weight standard curve. Folic acid was estimated microbiologically using Streptococcus faecalis strain R (ATCC 8043). Total amount of AIC and its riboside was determined by a modified Bratton-Marshall method (Stewart and Sevag, Arch. Biochem. and Biophys., 41, 9, 1952). Casein hydrolyzate (1 per cent) medium with glucose (0.5 per cent) was used for the growth of E. coli strain B. Adenine sulfate (20 Mug per ml) or p-aminobenzoic acid (PABA) (5 m,ug per ml) were added to the media for the growth, respectively, of purine requiring strain