Evaluation of Phagocytic and Bactericidal Activities of Neutrophil Granulocytes

Cefdinir-induced modification of the susceptibility of bacteria to the antibacterial activity of human serum and polymorphonuclear neutrophils

The effect of serum on the bactericidal activity of cefdinir, and the ability of the antibiotic to modify the interaction of bacteria with human polymorphonuclear neutrophils were assessed. In the presence of antibiotic, serum-resistant Escherichia coli were sensitised to the bactericidal activity of normal human serum. Cefdinir enhanced opsonophagocytic killing of Escherichia coli and Staphylococcus aureus at suprainhibitory concentrations. Significant potentiation of killing occurred with the combination of inhibitory concentrations of cefdinir, neutrophils and sub-optimal levels of serum opsonins. Pre-exposure of Escherichia coli, but not Staphylococcus aureus, to cefdinir enhanced phagocytic uptake and killing of the antibiotic-damaged bacteria. These results indicate that cefdinir-mediated phenotypic modification of Escherichia coli renders the bacteria susceptible to serum antibacterial activity and phagocytic uptake and intracellular killing.

Influence by staphylococcal lipase on granulocyte metabolism and killing of bacteria

Lipase purified from Staphylococcus aureus interferes with granulocyte phagocytic killing of S. aureus but not with killing of Streptococcus pneumoniae or Streptococcus agalactiae group B. Lipase treatment of granulocytes did not influence bacterial adherence to the cells.

Interference of Staphylococcus aureus lipase with human granulocyte function

The influence of purified Staphylococcus aureus lipase on granulocyte function and morphology was studied. The lipase itself was strongly chemotactic; in addition preincubation of granulocytes with low concentrations of lipase enhanced the directed movement, as assayed in the agarose system. Higher concentrations of lipase, in contrast, gave a progressive reduction of granulocyte chemotaxis; at 12 micrograms lipase per ml, cells were almost immobilized. Phagocytic killing of Staphylococcus aureus by granulocytes preincubated with lipase was reduced in a dose-dependent manner. At 12 micrograms lipase per ml almost no staphylococcal killing occurred. This was mainly accounted for by a reduction of bacterial uptake, but some decrease in intragranulocytic killing was also noted. These functional alterations, which can all be ascribed to an interference with membrane functions, were associated with marked changes of the granulocyte surface structure, which was denuded and lacked normal microvilli. The effects of lipase were partly retained after heat inactivation of lipase activity, indicating that the effects of staphylococcal lipase on granulocyte function are not due to enzymatic activity alone. These effects of lipase may be an important virulence factor and contribute to the preferential location of lipase-producing Staphylococcus aureus strains at deep sites of infection.

In vitro killing of erythromycin-exposed group A streptococci by polymorphonuclear leukocytes

After exposure to erythromycin, group A streptococci were tested for susceptibility to the antimicrobial activity of human peripheral blood neutrophils in the absence of the antibiotic. Bacterial susceptibility to phagocytic killing increased after prior exposure to supra-inhibitory levels of erythromycin for even as brief as three minutes. Extended exposure and higher concentrations of erythromycin increased phagocytic killing. Although the degree of sensitization varied in different strains of streptococci, all strains tested were significantly more susceptible to phagocytic killing after erythromycin exposure. Killing of erythromycin-treated bacteria that occurred in the absence of antibiotic was dependent upon internalization of the bacteria. Thus, the brief exposure of group A streptococci to inhibitory levels of erythromycin increases their susceptibility to phagocytic killing by peripheral blood neutrophils.

Cross-reacting opsonic antibodies to clinically important pneumococcal serotypes after pneumococcal vaccination

Opsonic activity of serum to pneumococcal serotypes 6 B, 9 V and 19 A was measured in 16 patients before and after immunization with a pneumococcal vaccine. The capsular polysaccharides of these serotypes are not included among, but are antigenically related to the vaccine polysaccharides. Patients responding to immunization with a twofold increase in serum antibodies to vaccine polysaccharides 6 A, 19 F and 23 F were studied. Increased opsonic activity towards serotypes 6 B, 9 V and 19 A was found in 12, four and ten patients respectively. In ten of the patients antibodies to serotypes 6 B, 9 V and 19 A were measured by a staphylococcal protein-A binding assay. A twofold increase in antibodies was found in postvaccination samples from ten, three and seven patients respectively. These results indicate that humans responding to pneumococcal vaccination, may also develop opsonic antibodies to other clinically important pneumococcal serotypes. The degree of cross-immunization appears to vary between individuals and between different pneumococcal serotypes.