Immunological specificity of natural opsonins and their role in the cross-reactivity between Staphylococcus aureus Mardi and Escherichia coli 101.

The immunochemical specificity of the observed cross-reactivity between Escherichia coli strain 101 and Staphylococcus aureus strain Mardi was examined. The cross-reactivity was shown to be dependent upon mucopeptide antibodies which are present in normal and immune sera. Although both organisms contained surface antigens with immunodominant glucuronic acid residues, in vitro phagocytosis studies indicated that antibodies directed against these antigens were not significantly involved in the opsonization process. Rather, antibodies with mucopeptide specificity were shown to be involved in the in vitro phagocytosis of these organisms by polymorphonuclear leukocytes. The mucopeptide antibodies, which were found in both nonimmune and immune sera, were shown to be effective in opsonizing both the S. aureus strain and the E. coli strain. The ubiquitous distribution of E. coli strains containing mucopeptide antigens common to most bacteria suggests that these organisms may be responsible for the wide prevalence of natural staphylococcal opsonins with mucopeptide specificity in normal sera.