Mode of action of the staphylococcin-like peptide Pep 5 and culture conditions effecting its activity.

Pep 5, a staphylococcin-like peptide produced by Staphylococcus epidermidis 5 was bactericidal for staphylococci and micrococci (Fig. 1). A stable L-phase variant of Staphylococcus aureus, but not of Streptococcus faecalis, was susceptible, too, indicating that the selectivity of Pep 5 is not due to the presence of a cell wall receptor. Addition of Pep 5 to cultures of the indicator strain caused immediate inhibition of DNA, RNA, protein, and polysaccharide synthesis (Fig. 5). The action of Pep 5 could be inhibited by increasing the cation content of the medium (e.g., to 100 mM Mg2+ or 600 mM K+) (Fig. 3), indicating a primary binding to anionic sites on the cell wall. Sublethally injured cells could be rescued by the addition of trypsin or 1 M KCl (Fig. 4).