Direct translocation of staphylococci from the skin surface to deep organs

• Staphylococcus aureus rapidly spread to deep organs in mice after skin inoculation.
• Blood cultures were negative in these experimental infections.
• Kidney histology was different after skin versus bloodstream infection.
• The skin infections caused death in mice with prolonged leucopenia.
• Thus, S. aureus can travel from skin to deep organs without bloodstream invasion.

BackgroundStaphylococcus aureus can invade the bloodstream and cause bacteremic infections, but this organism frequently produces serious deep infections without bacteremia or an identifiable portal of entry.MethodsWe used experimental cutaneous S. aureus infections in mice to determine if the bacteria could reach deep organs without travel through the bloodstream.ResultsAfter skin surface application the bacteria rapidly distributed to lymph nodes, spleen, kidneys and other organs. In these animals, blood cultures were negative, dissemination was more efficient after surface application than injection near dermal blood vessels, and kidney bacterial localization sites were unlike those of bacteremic infections. Whereas normal mice eventually cleared bacteria from the deep sites, those with prolonged immunosuppression became moribund from these infections; they also had negative blood cultures and kidney localization not consistent with hematogenous dissemination. Bacteria were also found in the intervening abdominal wall outside the spleen and kidney sites, suggesting direct movement of the organisms from the skin surface through connecting tissues.ConclusionsAlthough capable of hematogenous dissemination, S. aureus can also spread from skin to deep organs by a non-bacteremic process. In this case the bacteria appear to migrate directly from the skin surface to the deep organs below.