The use of lysostaphin in in vitro assays of phagocyte function: adherence to and penetration into granulocytes

The usefulness of lysostaphin for the removal of cell-adherent and extracellular bacteria in assays performed to measure the intracellular killing of Staphylococcus aureus by granulocytes was investigated. The results showed that the adherence of lysostaphin to the granulocyte surface is effectuated by a temperature-independent process and that bound lysostaphin is still microbicidal. Lysostaphin also penetrates into the granulocytes by a temperature-dependent process and kills ingested S. aureus intracellularly. Therefore, despite reports to the contrary in the literature, lysostaphin is not a reliable agent for the removal of only extracellular S. aureus and should no longer be used in assays to determine the rate of intracellular killing by granulocytes.