Previous studies have shown that when Staphylococcus aureus becomes resistant to sulfonamides, an antisulfonamide substance is produced in the growth medium. Although these studies suggested that the substance was p-aminobenzoic acid (PABA), isolation and positive identification were not achieved. Because of the importance of these observations, unequivocal identification of the product was attempted.
A strain of Stapkylococcus aureus resistant to sulfonamides was cultivated on a simplified medium, the organisms separated in a Sharples centrifuge and the diazotisable amine absorbed on amberlite IR-120 previously acidified. Elution was accomplished with pyridine and the amine recovered by ether extraction at pH 3.7. Paper chromatography revealed one amine resembling PABA and another contaminating diazotizable amine present in very small amounts. The PABA-like amine was further separated by chromatography; its Rf value and its spectrum in the ultraviolet then equalled those obtained with PABA. A 2,4-dlnltrophenyl derivative of the amine was prepared and the m.p. was similar to that of the derivative made from PABA.
On the basis of the physical and chemical properties described, it would appear unequivocal that this bacterial amine is PABA.