Effects of sucrose and silver on Staphylococcus aureus biofilms

The present study examined the effects of antimicrobial agents on a biofilm model of Staphylococcus aureus. A membranous structure (an immature biofilm) was formed on the coverslips of tissue culture dishes by S. aureus cells in plasma after incubation for 24 h. After incubation, the colony counts of S. aureus cells in the immature biofilms in plasma containing levofloxacin with 70% sucrose were about one-tenth of those in plasma containing levofloxacin without sucrose. The colony counts of S. aureus cells in the immature biofilms in plasma containing silver sulphadiazine or silver nitrate (at a silver concentration of 0.302%) were over 3000 times lower than those in control plasma without silver after incubation for 24 h. Plasma coagulation by S. aureus cells was not detected in plasma containing 70% sucrose 48 h after inoculation. The immature biofilms were incubated in plasma with and without 70% sucrose, and the immature biofilms were treated with 10% povidone-iodine for 2 min after incubation for 4 and 16 h. In this experiment, the colony counts of S. aureus cells in the immature biofilms incubated with 70% sucrose were about one-tenth of those in plasma without sucrose after incubation for 24 h. We suggest that levofloxacin or 10% povidone-iodine in combination with 70% sucrose and silver sulphadiazine or silver nitrate (at a silver concentration of 0.302%) are effective in eliminating S. aureus cells in a biofilm.