HOST RESISTANCE TO SERRATIA-MARCESCENS INFECTION - SERUM BACTERICIDAL ACTIVITY AND PHAGOCYTOSIS BY NORMAL BLOOD LEUKOCYTES

Abstract

S. marcescens strains isolated from clinical specimens can be divided into those which are sensitive or resistant to the bactericidal activity of normal human serum. Serum bactericidal activity is heat labile, cation dependent and is absorbable by whole serum-sensitive Serratia or ethanol-insoluble extracts of these organisms. Bacteremic Serratia infection is invariably caused by the serum-resistant strains. Serum resistant Serratia are ingested and killed by normal human leukocytes and fresh normal serum. Heating or preabsorption of serum with whole, heat-killed or ethanol-insoluble antigen extracts of the serum-resistant Serratia diminishes opsonization and phagocytosis. Serratia opsonins in the serum of healthy individuals are type-specific immunoglobulinM globulins which combine with the organism and activate complement by the alternate pathway.