Staphylococcus epidermidis

Bacteria, including E. coli (KCTC 1682), Staphylococcus typhimurium (KCTC 1926), Pseudomonas aeruginosa (KCTC 1637), Bacillus subtilis (KCTC 3068), Staphylococcus epidermidis (KCTC 1917), and S. aureus (KCTC 1621) were procured from the Korean Collection for Type Cultures (KCTC) at the Korea Research Institute of Bioscience and Biotechnology (Deajeon, South Korea). MRSA strains (CCARM 3089, CCARM 3090, and CCARM 3095) were obtained from the Culture Collection of Antibiotic-Resistant Microbes (CCARM) at the Seoul Women's University (Seoul, South Korea). All bacteria were routinely grown at 37°C in Luria-Bertani broth. MICs were measured in 96-well microplates using the micro-broth dilution method. Bacteria were grown in Luria-Bertani broth at 37°C for 18 h and then diluted with 1% peptone to a final concentration of 2 × 10 6 colonyforming units per ml. Subsequently, 100 µl of a bacterial suspension and 100 µl of peptide solution were mixed together in a 96-well plate. The peptide solution was prepared by performing two-fold dilutions in 1% peptone, while the PGP-E solutions were prepared to final peptide concentrations of 0.06-128 µg ml -1 . The bacteria and peptide solution mixtures were incubated at 37°C for 18 h. The peptide MIC was defined as the lowest concentration of peptide that inhibited bacterial growth.

The six strains used in this study are common skin microflora. They included four gram-positive strains and two yeasts. Malassezia furfur (KCTC 7743) and Malassezia globosa (KCTC 7846) , which cause dandruff, Corynebacterium xerosis (KCTC 9105) , which causes underarm malodor, and Staphylococcus aureus (KCTC 6538) and Staphylococcus epidermidis (KCTC 13170) , which are typical skin microorganisms, were obtained from the Korean Collection for Type Cultures (KCTC, Jeongeup, Jeonbuk) . Corynebacterium jeikeium (ATCC 43734) was obtained from the American Type Culture Collection (ATCC, Manassas, VA) . Before use, the Malassezia species were each inoculated on Leeming and Notman (LN) medium and incubated for 1 d in orbital shakers at 30℃. The other four strains of bacteria were inoculated onto Brain Heart Infusion (BHI, BD, Sparks, MD, USA) media and incubated for 1 d in an orbital shaker at 35℃.