A loop of S. aureus was transferred from the nutrient agar slant to 100 mL of nutrient broth and inoculated at 37 °C for 16 h as the stock culture. For the preparation of the inoculum, S. aureus was prepared by inoculating nutrient broth (100 mL) with 1 mL of stock culture and incubating at 37 °C for18 h with shaking at 200 rpm. During the growth of S. aureus, early stationary cells were harvested by centrifugation at 7000 × g at 4 °C for 15 min and then washed twice with a 0.85% sterile saline solution and pelleted again. S. aureus suspensions had a population of ca. 7 log CFU/mL.