Inhibition of the biosynthesis of cell-wall mucopeptides by the penicillins. A study of penicillin-sensitive and penicillin-resistant strains of Staphylococcus aureus

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Abstract
The concentration of benzylpenicillin required to inhibit cell-wall-mucopeptide formation by Staphylococcus aureus strain Oxford is of the same order as that required to prevent growth. Benzylpenicillin-resistant cells selected on artificial media from the original culture require very much higher concentrations of the antibiotic to inhibit cell-wall-mucopeptide formation. The composition of the cell walls of the sensitive and resistant cells is the same. The inhibitory effects upon mucopeptide synthesis by sensitive cells of sodium 6-(2,6-dimethoxybenzamido)penicillin (Methicillin), 6-([alpha] phenoxypropionamido)penicillanic acid (Broxil) and 6-aminopenicillanic acid are as predicted from their relative potencies tested as antibiotics. Cells made resistant to benzylpenicillin do not require increased concentrations of sodium 6-(2, 6-dimethoxybenzamido)penicillin to inhibit mucopeptide synthesis. Sodium 6-(2, 6-dimethoxybenzamido)penicillin, like benzylpenicillin, does not inhibit the formation of either proteins or nucleic acids by S. aureus. Sodium 6-(2, 6-dimethoxybenzamido) penicillin inhibits almost completely mucopeDtide synthesis by the penicillinase-producing strain S. aureus 524/SC. The concentration required is similar to that needed by the sensitive strain Oxford.