Variability in the degree of opsonization and phagocytosis of strains of Staphylococcus aureus isolated from patients with disseminated intravascular coagulation.

Patients with septicemia due to Staphylococcus aureus occasionally manifest DIC. We studied the ability of organisms isolated from 30 patients with S. aureus (5 with DIC) to be opsonized and phagocytosed by normal human PMNs in the presence of normal human serum chelated with MgEGTA as a possible measure of alternative complement pathway activation. By this assay, nine S. aureus strains were found to be opsonized at 50% level or greater. Five of those organisms were isolated from the five patients who had clinical and laboratory manifestations of DIC, three of whom died. Patients from whom the other four activating strains were isolated were more seriously ill (by a method of grading clinical severity of disease) than the remaining 21 patients. Four of the nine patients from whom activating strains were isolated died compared to only four of the other 21 patients. The accelerated phagocytosis of staphylococcal strains from patients with DIC after incubation in MgEGTA-chelated serum suggests that surface factors on these strains interacted with serum factors differently than did strains from patients not developing DIC. However, all (except one) staphylococcal strains, from patients both with and without DIC, depleted hemolytic complement activity in MgEGTA-chelated serum; therefore a direct relationship between activation of the alternative complement pathway and opsonization seems not to exist. Thus strains of S. aureus capable of being opsonized by PMNs in human serum chelated with MgEGTA were associated with more severe infections often associated with DIC.