Expression of lysostaphin in HeLa cells protects from host cell killing by intracellular Staphylococcus aureus

The Staphylococcus aureus-specific cell wall endopeptidase lysostaphin was used as a model for an intracellular acting bactericidal antibiotic. HeLa cells were transfected with an expression vector directing the heterologous expression of lysostaphin in the cytoplasm. Expression, subcellular localization and enzymatic activity of lysostaphin were investigated by immunoblotting, fluorescent microscopy and agar diffusion assays. Both transiently and stably transfected HeLa cells showed a strong expression of active lysostaphin. After infection with S. aureus, the intracellular number of S. aureus and the host cell viability were determined. This staphylolytic activity resulted in a strong reduction of intracellular S. aureus in a time- and dose-dependent manner. Furthermore, host cells expressing lysostaphin became protected from S. aureus-induced cell death. Our data demonstrate the potential of intracellularly acting cell-wall active drugs or antibiotics that kill S. aureus without causing harm to the infected host cells.