Activity of Staphylococcus epidermidis phenol-soluble modulin peptides expressed in Staphylococcus carnosus

Staphylococcus epidermidis releases a group of peptides termed phenol-soluble modulin (PSM) that stimulate macrophages. The structure of 3 peptides (PSMalpha, PSMbeta, and PSMgamma) have been described. We report a fourth peptide (PSMdelta), which is a 23mer with the structure fMSIVSTIIEVVKTIVDIVKKFKK. The gene for each of the 4 peptides was introduced singly into Staphylococcus carnosus, and the PSM-like activity of culture medium and bacterial extract were significantly greater than those of the parent strain. PSM peptides from each of the S. carnosus - expressing strains were purified and analyzed by liquid chromatography - mass spectrometry. The products, which appeared to form aggregates, were active in the activation of human immunodeficiency virus type 1 long-terminal repeat and the production of tumor necrosis factor - a by the macrophage cell line THP-1. These findings suggest that PSM peptides are responsible, in part, for the modulin-like activity of staphylococci and may contribute to the development of severe staphylococcal sepsis.