The surface protein Pls of methicillin-resistant Staphylococcus aureus is a virulence factor in septic arthritis

Pls, a surface protein of certain methicillin-resistant Staphylococcus aureus strains, is associated with poor bacterial adherence to solid-phase fibronectin and immunoglobulin G, as well as with reduced invasion of cultured epithelial cells. Here the importance of Pls for the development of septic arthritis and sepsis was investigated by using a mouse model. Mice inoculated with a pls knockout mutant developed a much milder arthritis and showed less grave weight reduction than mice infected with the wild-type Pls(+) clinical isolate. Also, the pls mutant induced a significantly lower frequency of mortality than the wild-type strain. The bacterial load of the kidneys was larger in mice infected with the Pls(+) strain than in animals challenged with the pls mutant. However, there was no evident inflammatory effect due to the Pls molecule alone, as indicated by knee injection of purified Pls. In conclusion, the results show that Pls is a virulence factor for septic arthritis and sepsis.