Role of Escherichia coli alpha-hemolysin and bacterial adherence in infection: requirement for release of inflammatory mediators from granulocytes and mast cells.

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We investigated the role of bacterial mannose-resistant fimbriation of S fimbriae (Fim), mannose-resistant hemagglutination (S-Mrh), and hemolysin (Hly) production by an Escherichia coli parent and genetically cloned strains as regards their effect on histamine release from rat mast cells and generation of the chemiluminescence response, leukotriene, and enzyme release from human polymorphonuclear granulocytes. These mediators are involved in the induction of inflammatory disease processes and lead, e.g., to the enhancement of vascular permeability, chemotaxis, aggregation of granulocytes (leukotriene B4), lysosomal enzyme release, and smooth-muscle contraction (leukotrienes C4, D4, and E4). The content of azurophilic and specific granules in polymorphonuclear granulocytes consists of highly reactive enzymes which amplify inflammatory reactions. Washed bacteria (E. coli 764 Hly+/-, E. coli 21085 Hly+/- Fim+/- Mrh+/-), as well as their culture supernatants, were analyzed at various times during their growth cycle. No differences exist between parent and cloned or mutant strains with respect to their outer membrane proteins and lipopolysaccharide pattern. Washed bacteria [E. coli 764 and 21085(pANN202-312)] which produced hemolysin, unlike Hly- strains, induced high levels of histamine release from rat mast cells and led to a significant chemiluminescence response and enzyme and leukotriene release from human polymorphonuclear granulocytes. Bacterial culture supernatants from Hly+ and secreting strains showed similar results with the exception of E. coli 21085(pANN202-312), which is a hemolysin-producing but not a secretory strain. Our data suggest a potent role for hemolysin as a stimulus for noncytotoxic mediator release from various cells. Furthermore, we showed that the presence of Fim and S Mrh potentiates mediator release. The simultaneous presence of Mrh and Fim [E. coli 535/21(pANN801-4)] increased mediator release compared with Mrh+ Fim- strains [E. coli 536/21(pANN801-1)]. E. coli 536/21 (Msh- Mrh- Fim- Hly-) did not induce mediator release.

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