Alginic acid was purified from a mucoid clinical isolate of Pseudomonas aeruginosa. Luminol-dependent chemiluminescence of phorbol myristate acetate-stimulated neutrophils was inhibited by this alginate, but oxygen consumption was unaffected. Further studies indicated that this effect was due to the ability of the pseudomonal alginate to scavenge hypochlorite. A seaweed alginate was less effective and dextran T500 was ineffective in hypochlorite scavenging. It appears that the uronic acid core and the O-acetyl groups of pseudomonal alginate are involved in its hypochlorite-scavenging ability. The relevance of this phenomenon was demonstrated by the greater resistance to killing by hypochlorite of mucoid P. aeruginosa compared with a nonmucoid revertant, and the addition of purified alginate to the nonmucoid revertant protected the organism from hypochlorite. Thus, this extracellular polysaccharide may enhance the virulence of P. aeruginosa by scavenging the phagocyte-generated oxidant HOCI. This enhanced virulence may be involved in disease processes in which mucoid organisms predominate, such as cystic fibrosis.
The serum antibody response of patients infected with alpha-hemolysin (AH)-producing Escherichia coli was measured by three immunoassays: tube neutralization, microneutralization, and enzyme-linked immunosorbent assay. All three assay results showed good correlation with each other. The mean anti-AH titer in patients with E. coli infection was higher than the mean titer in noninfected patients. The hemolysin-neutralizing activity was immunoglobulin G. The amount of lipopolysaccharide (LPS) antibody did not correlate with the amount of AH antibody. LPS antibody measured by enzyme-linked immunosorbent assay was predominantly of the immunoglobulin G class. Adsorption of LPS antibody by E. coli H79 LPS did not affect anti-AH titers, indicating that LPS and AH have different antigenic determinants. AHs prepared from several different E. coli strains had identical or similar antigenic determinants at the active site. Hemolysin proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were stained identically by human sera with AH antibody and by a mouse monoclonal AH antibody.
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