Electron Microscopic Studies on Streptococci

Abstract

Extensive chemical and immunological studies have characterized the group A streptococcal cell wall as composed of four major components: M protein (and related T and R antigens), carbohydrate, mucopeptide, and glycerol teichoic acid (1, 2). These cell wall constituents, along with an external capsule and an underlying cytoplasmic membrane, are important in determining the relationship between group A streptococci and their human hosts (3). Our aim is to define the morphology and location of each of the major components of the streptococcal cell wall. The first component we have studied is the M antigen or M protein, the topic of this report.M protein plays a role in determining virulence of streptococci, inhibits phagocytosis of the organisms by leukocytes, and stimulates production of type-specific, protective antibodies by the animal host (4). These effects, together with other properties attributable to the protein, have suggested to previous investigators that the M antigen is on the exterior of group A streptococci (1, 4). Our electron microscopic findings substantiate this concept. We have found that the presence of M antigen is associated with hair-like fimbriae on the outer surfaces of several strains of group A streptococci. It appears that multiple M antigenic sites reside along the length of the fimbriae. R antigens may be associated with the same type of fimbriae. We have also obtained data suggesting the attachment of the M-associated fimbriae to the underlying portions of the cell wall. Finally, our studies suggest that M protein is not incorporated into the cell wall simultaneous to the synthesis of other portions of the wall.

The capsules of Corynebacterium equi and Streptococcus equi

“…Outside the wall only short thick projections were seen, with no layer external to them. These projections in no way resembled the surface fimbriae which have been demonstrated in group A streptococci (Swanson et al, 1969). When ruthenium red was not used for staining, no structures were visible external to the wall.…”

Mediation of Cytotoxic Effects of Streptococcal M Protein by Nontype-Specific Antibody in Human Sera

“…To determine whether the NTSAI antigen(s) represented a deeper structure of the cell wall or, perhaps, an extension of the underlying protoplast +Type 24 streptococci that lost their resistance to phagocytosis after multiple subculttires in laboratory media. membrane through the cell wall, fresh human serum, which contained NTSM antibody, was absorbed with 2 mg /ml of cell walls, purified cell wall mucopeptide, or protoplast membranes (Table VIII).…”

“…These fimbriae-like structures (3,24) appear to carry the unique TSM antigenic determinant that is exposed on the surface of fully "virulent" organisms. The deeper NTSM-associated part of the fimbriae may arise at the protoplast membrane and may be continuous with, but lie proximal to, the TSM.…”

Streptococcal Rheumatic Carditis.

“…Fimbriae could possibly represent slender extensions of the membrane that penetrate the cell wall. This particular cellular location of the membrane antigens might explain why past attempts to clearly separate wall and membrane antigens have not been fruitful (166,256). Dale and Beachey (51) recently showed that a purified preparation of group A streptococcal type 5 M-protein contained an antigen within it which elicited heart reactive antibody, implying that it was the component responsible for cross-reactivity.…”

“…Both antigens were shown to absorb heart antibodies from human sera (16). The possibility was therefore considered that the same antigen(s) was present on protoplast membranes as well as on the fimbriae-like structures that protrude through the cell wall and that contain Mprotein (256). It has been speculated that membrane antigens (fimbriae) are present at the outer surface of the cell, a location that might contribute to their antigenicity.…”