Action of Quinacillin on Staphylococcus aureus

Abstract

QUINACILLIN, the disodium salt of 3-carboxy-2-quinoxalinylpenicillin, has recently been described^1,2 and has, for a penicillin, unusual properties. The striking feature is the pattern of the antibacterial spectrum which shows that quinacillin is significantly active (0.15–0.62 µg/ml., 0.32–1.35 µM) against Staphylococcus aureus (Oxford strain) but that a 10–100-fold increase in concentration is necessary before activity against other Gram-positive organisms can be demonstrated. It seemed profitable, therefore, to compare the action, if any, of quinacillin on causing the intracellular accumulation of N-acetylamino sugars and to compare this quantitatively with benzyl-penicillin as evidence of a typical penicillin-like mode of action^3,4. Staphylococcus aureus was growrn for 18 h in a medium containing yeast extract 5 g peptone, 5 g glucose, 2 g K₂HPO₄, 1 g water to 1 1. In the middle of the logarithmic growth the penicillin was added and after 90 min the intracellular acetylaminosugar was determined colorimetrically⁵. Results are shown in Fig. 1.