Laboratory of Bacterial Pathogenesis and Immunology

(28,000X)

Negative staining of group A streptococci viewed by TEM. The "halo" around the chain of cells (approximately equal in thickness to the cell diameter) is the remnants of the capsule that may be found surrounding the exterior of certain strains of group A streptococci. The septa between pairs of dividing cells may also be seen.

A capsule is characteristic of some strains of pathogenic streptococci, including members of group A and group C. The capsule is composed of hyaluronic acid.