Production and partial purification of a peptide antibiotic from Staphylococcus epidermidis

When grown on solid or in liquid Brain Heart Infusion at 37 degrees C, Staphylococcus epidermidis NCIB 11536 produced antibiotic activity against a wide range of Gram positive bacteria. Production was influenced by aeration, pH, glucose concentration and specific growth rate. Inhibitory activity could be concentrated by ammonium sulphate precipitation (30-55% saturation). On Sephadex G50 using 0.05 mol/l sodium phosphate buffer, pH 6.0, two peaks of antibiotic activity were detected. The first peak eluted with the void volume (Kd = 0) and the second peak was retained by the gel (Kd = 0.73-0.77). These two substances did not represent the monomeric and polymeric forms of a staphylococcal bacteriocin. The low mol. wt inhibitor, which was responsible for over 95% of the recovered activity on Sephadex G50, could be partially purified by a combination of gel filtration on Biogel P2 and ion-exchange chromatography on Sephadex C-25. Yields were increased by combining these two steps into a single procedure (duocolumn). The semi-purified inhibitor was desalted using Sep-pak C18 cartridges. Biological activity was resistant to enzymic denaturation except by high concentrations of trypsin (50 units/micrograms, 3 h, 25 degrees C). This peptide antibiotic is different from any previously described staphylococcal inhibitors.