Sensitivity of K1-Encapsulated Escherichia coli to Killing by the Bactericidal/Permeability-Increasing Protein of Rabbit and Human Neutrophils

Abstract

The presence of K1 capsular polysaccharides increases the resistance of Escherichia coli to killing by serum and phagocytosis by polymorphonuclear leukocytes (PMNs). To determine whether K1 capsule impedes the action of intracellular bactericidal systems of PMNs, we compared the sensitivity of several K1-encapsulated and non-encapsulated strains of E. coli to killing by the bactericidal/permeability-increasing protein (BPI) isolated from rabbit and human PMNs. BPI appears to be the principal bactericidal agent of PMNs toward E. coli and other gram-negative bacteria (Weiss et al., J. Clin. Invest. 69 :959-970, 1982). The presence of K1 capsule was monitored by sensitivity to K1-specific bacteriophages. The non-encapsulated strains used represent both random bacteremic isolates and non-encapsulated derivatives of K1-encapsulated strains obtained by selection for resistance to K1-specific phages. We found little or no difference in the sensitivity of K1-encapsulated and non-encapsulated E. coli to killing by neutralized acid extracts of rabbit PMNs. Bacterial killing by these crude fractions can be attributed to the action of BPI because: (i) bacterial killing was blocked by immune (anti-BPI) immunoglobulin but not by preimmune immunoglobulin and (ii) comparison of the dose-response curves of bacterial killing by crude extracts and by purified BPI showed that the bactericidal activity of crude fractions corresponded closely to the BPI content. Human and rabbit BPIs exhibited similar bactericidal potency toward K1-encapsulated E. coli ; i.e., <5 μg of either protein killed >90% of 2.5 × 10 7 bacteria. Thus, the potent bactericidal action of BPI toward E. coli is not impeded by K1 capsule, suggesting that the virulence of K1-encapsulated E. coli is a consequence of extracellular survival but not of resistance to intracellular killing.

Loss of the O4 antigen moiety from the lipopolysaccharide of an extraintestinal isolate of Escherichia coli has only minor effects on serum sensitivity and virulence in vivo

“…Its specific role will undoubtedly be clarified with further in vitro and in vivo evaluations. A number of previous studies have suggested that the LPS is an important factor in protecting against the effects of bactericidal/permeability-increasing protein (42,43). Studies with our isogenic O4 antigen mutants support this contention (24a).…”

Cationic antimicrobial proteins isolated from human neutrophil granulocytes in the presence of diisopropyl fluorophosphate

“…The involvement of cationic proteins derived from the cytoplasmic granules in killing bacteria has been recognized in the PMN systems of rabbits (3,21,(23)(24)(25)(26)(27)(28)(29), guinea pigs (30), rats (5), cows (4) and humans (8,10,22,25,27,28). However, the biochemical nature of such proteins derived from all PMN species have remained uncertain.…”

“…Cationic proteins (8,10,12,13,15,(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) derived from polymorphonuclear granulocyte (PMN) cytoplasmic granules appear likely to mediate oxygen-independent, intraleukocytic killing of bacteria (7). Earlier studies (8,12,13,15,22) dealing with human PMNs have documented the role of lipopolysaccharide (LPS) in the determination of the phenotypic level of resistance of gram-negative bacteria to both granule extracts and more-purified cationic antimicrobial proteins (CAPs); that is, deep rough mutants containing truncated LPS were less resistant to CAPs than was the isogenic smooth parental strain.…”

Shigella flexneri is trapped in polymorphonuclear leukocyte vacuoles and efficiently killed

“…The total incubation volume was 0.1 ml. To determine the role of the BPI in the antibacterial activity of the PMN extracts, the extract was preincubated with 3% (vol/vol) goat serum (nonimmune or anti-BPI) for 15 min at room temperature, as described previously (25,28), before the addition of bacteria. Samples were incubated for 1 h at 37ЊC with shaking.…”