Interaction of Staphylococcus epidermidis with endothelial cells in vitro

Staphylococcus epidermidis is a leading cause of nosocomial bacteremia, yet virtually nothing is known about how this pathogen interacts with human endothelial cells. We present evidence here that two biofilm-producing strains of S. epidermidis adhere to two types of endothelial cell lines in vitro and that adherence is significantly increased after briefly heat-treating the bacteria at 40 degrees C in the presence of calcium. This mild heat treatment resulted in bacteria that were 5 to more than 20 times more adherent than untreated controls. While the adherence of bacteria in all phases of growth was increased after heat treatment, heat-treated late stationary phase cells were generally the most adherent. Electron microscopy demonstrated that S. epidermidis was internalized and appeared to exist free in the cytoplasm. Adherence to endothelium, should it occur in vivo during bacteremia, may be a virulence factor associated with this bacterium's pathogenesis.