Sophorolipids as antibacterial agents.

Sophorolipids (SLs), glycolipids produced by yeasts, have been reported to have immunomodulating activity and to reduce the mortality rate in animal models of sepsis. In the present study, the antibacterial activities of SLs and several derivatives were tested against a selection of standard bacterial isolates using the broth microdilution method. The SL derivatives tested did not show any significant antibacterial activity in vitro when tested at clinically relevant concentrations. Most likely the reported decrease of mortality rate in the rat septic shock model was not secondary to antibacterial activity of SLs. The SLs may be used as anti-inflammatory agents or immunomodulators without affecting the host's bacterial flora.