Electron microscopy of group A streptococci after phagocytosis by human monocytes.

Group A streptococci were added to cultures of isolated human blood monocytes. The bacteria were readily sequestered within phagocytic vacuoles after being coated with flocculent material, apparently derived from the plasma-containing medium. Progressive lysis of intravacuolar streptococci was observed, characterized by plasmolysis, internal disruption, and eventual plasma membrane dissolution. However, the cell walls remained essentially identical to those of nonphagocytized streptococci, showing no signs of dissolution within the limited in vitro survival time of the monocytes. These results indicate that streptococcal cell walls may persist in migrating human phagocytes in vivo and may be deposited in body tissues. This cell wall material, known to be toxic to animal tissues, may be an important determinant in the pathogenesis of poststreptococcal sequelae in man.