Effects of Pseudomonas aeruginosa rhamnolipids on human monocyte-derived macrophages

Pseudomonas aeruginosa, a major opportunistic gram-negative pathogen, produces and secretes two heat-stable hemolytic glycolipids, a monorhamnolipid and a dirhamnolipid. In this paper a simplified method for the isolation of these rhamnolipids is described. The effect of these two rhamnolipids, both together and individually, on the viability and structural morphology of human monocyte-derived macrophages (MDMs) was examined. These cells were found to be very susceptible to the cytolytic activity of the rhamnolipids, particularly the dirhamnolipid. The monorhamnolipid, although not as cytolytic as the dirhamnolipid, caused extensive blebbing of the MDM plasma membrane. Comparison studies with several detergents confirmed the different yet distinct detergent-like activity of each rhamnolipid form. At sublethal doses, the rhamnolipids produced marked cellular distortions of the MDMs and inhibited the ability of these cells to bind and/or ingest preopsonized bacteria. The potential mechanism of action of these rhamnolipids on the MDM membranes is discussed, as well as the possible significance of these extracellular bacterial glycolipids as a virulence factor in the pathogenesis of P. aeruginosa.