Effect of phenolic compounds on the adenosine triphosphatase of the membrane of Staphylococcus aureus

Butylated hydroxyanisole (BHA) and tertiary butylhydroquinone (TBHQ) were found to be effective inhibitors of the growth of Staphylococcus aureus. The minimum inhibitory concentrations (MIC) were 150 ppm BHA and 25 ppm TBHQ for the four strains tested. When the strains were grown in 250 ppm BHA, strain LP was found to be more resistant than the other three strains studied. Therefore, strain LP was chosen as the more resistant strain and strain A100 as the more sensitive one for the ATPase activity studies. Cytoplasmic membranes of late-exponential phase cells of both strains were isolated after digestion of the cell wall with lysostaphin by osmotic lysis and centrifugation. Membrane prepara-tions isolated from strain LP and A100 contained 46.5% protein, 25.7% lipids, 3.1% carbohydrates, 8.1% RNA and 0.6% RNA, and 49.8% protein, 30.9% lipids, 3.9% carbohydrates, 8.6% RNA and 0.7% DMA, respectively. The optimal conditions for the ATPase assay were determined. The reaction mixture used contained 150 mM K⁺ and 2.5 mM MgATP in 50 mM TRIS-acetate buffer (pH 6.0). Na⁺ was less stimulatory than K⁺. Neither Mg⁺² nor Ca⁺² were found to stimulate the ATPase of S. aureus. This might be due to the fact that the substrate used was MgATP. Among the four phenolic antioxidants studied, only BHA was found to stimulate the ATPase activity of both strains at concentrations greater than the MIC. While butylated hydroxytoluene (BHT) did not have any effect on the ATPase at the concentrations studied, TBHQ and propyl gallate (PG) inhibited the activity of this enzyme. In general, the three derivatives of the hydroxycinnamic acid studied, p-coumaric, ferulic and caffeic acid, were inhibitory to the ATPase of S. aureus, the first being the most inhibitory. The methyl and propyl parabens did not affect the ATPase activity of the strains studied. A significant difference was found between the two strains studied. The ATPase isolated from strain LP was less stimulated by BHA than that from strain A100, while it was more inhibited by TBHQ and PG. However, this enzyme was less inhibited by p-coumaric acid than the enzyme isolated from strain A100. Moreover, it was not affected by either ferulic or caffeic acid.