Determinants of the biologic activity of surface slime in experimental Pseudomonas aeruginosa infections

A purified fraction of the extracellular slime of Pseudomonas aeruginosa, characterized chemically as a glycolipoprotein (GLP), has been identified as responsible for a number of biologic properties of the viable cell. Mice immunized actively or passively against GLP are protected against an otherwise lethal challenge with viable bacteria. GLP is chemically, physically, and antigenically distinct from the lipopolysaccharide of the same strain. An in vivo association of GLP with blood leukocytes has been demonstrated, and the leukopenia in mice following challenge with P. aeruginosa may be accounted for by the subsequent sequestration of a neutrophil-GLP complex in the liver. Anti-GLP serum in the absence of complement mediates the phagocytosis and eventual killing of viable P. aeruginosa by mouse polymorphonuclear leukocytes and unstimulated peritoneal macrophages. A polysaccharide fraction isolated from the GLP is responsible for its protective immunogenicity. Although the lipid moiety governs the leukopenic and lethal capacities, the carbohydrate, specifically the mannose of this moiety, is required for full expression of GLP lethality. Mannose is also an immunodominant sugar.