Mode of antibacterial action of a signal peptide, Pep²⁷ from Streptococcus pneumoniae

The aim of this study was to assess the in vitro antimicrobial activity of Pep²⁷ and its mode of action. The results indicated Pep²⁷ exhibited antibacterial activities against pathogenic Gram-positive and Gram-negative bacteria without hemolytic effect on human erythrocytes, but it did not exhibit antifungal activity. To understand the mode of action of Pep²⁷, the cellular distribution of the peptide was investigated. Flow cytometry analysis exhibited Pep²⁷ penetrated the bacterial membrane by an energy-independent pathway without any damage to the membrane when examined using liposome and membrane probe. After penetration into the bacterial cells, Pep²⁷ was not affected by macromolecular synthesis, but activated protein phosphatase activity in dose ranges of 10-15 μM and time range of 5-10 min in case of Staphylococcus epidermidis and Pseudomonas aeruginosa, respectively. These results demonstrated the antibacterial activities of Pep²⁷ are fundamentally attributable to a physiological change by activated phosphatase activity.