FIG. 2.

Cross-inhibition of S. epidermidis and S. aureus by agr pheromones. The amount of delta-toxin in 500 μl of supernatant was determined by high-performance liquid chromatography after 8 h of growth and under the influence of different concentrations of added pheromone or pheromone derivatives. Pheromones were diluted in dimethyl sulfoxide; the control received only dimethyl sulfoxide. Cultures were grown in basic medium (1% tryptone [Difco], 0.5% yeast extract [Gibco BRL], 0.5% NaCl, 0.1% K₂HPO₄, 0.1% glucose) with shaking at 37°C. (A) Effect of the S. epidermidis pheromone on delta-toxin production of S. aureus agr subgroups. (B) Effect of the pheromones of different S. aureus agr subgroups on delta-toxin production of S. epidermidis.