CONTRIBUTION OF ANTIBODY TO NEUTROPHIL-MEDIATED KILLING OF ENTEROCOCCUS-FAECALIS

Late-onset septicemia due to Enterococcus faecalis is common among ver y low-birth weight neonates. These infants have low concentrations of placentally derived IgG and developmentally low levels of complement. The aim of the present study was to determine the contribution of anti body to in vitro neutrophil-mediated phagocytosis of E. faecalis. Anti body alone, as contained in an adult serum pool heated to inactivate c omplement, promoted only a modest reduction in the initial bacterial i noculum (50 +/- 12%) for 6 of 10 E. faecalis bacterial strains tested and allowed growth of the other four strains. In the presence of compl ement, NHS promoted greater than or equal to 90% reduction in the init ial bacterial inoculum of two representative strains at serum concentr ations as low as 0.5%. Hypogammaglobulinemic serum supported similar a ctivity only at concentrations above 5%. Purification of IgG and IgM f ractions from NHS revealed that IgM had the higher specific activity t o promote phagocytic activity. Absorption to remove specific antibody significantly reduced bactericidal activity by normal human serum, com plement-deficient sera, and hypogammaglobulinemic serum. Reconstitutio n of hypogammaglobulinemic serum with antibody as contained in 1% heal ed normal human serum or in immune globulin for intravenous use (1200 mg/dl) restored phagocytic activity. Thus, E. faecalis-specific antibo dy enhances PMN-mediated killing of this organism. Adjunctive therapy with intravenous immunoglobulin could augment the host response to ent erococcal infections in infancy.