Bacterial ultrastructure is concerned with the cellular and molecular construction of bacteria. The bulk of research in bacterial ultrastructure investigates the ultrastructure of the cell wall that surrounds bacteria.

The study of bacterial ultrastructure began with the development of the staining regimen by Danish pathologist Christian Gram (1853-1938) that classifies the majority of bacteria as either Gram-negative or Gram-positive. The latter bacteria retain the crystal violet stain, while Gram-negative bacteria do not retain this stain and are stained by the second stain that is applied, safranin. While the basis for this difference was not known at first, scientists suspected that the structure of the wall surrounding the contents of the bacteria might be involved.

Subsequent to the time of Gram, scientists have discovered that the cell wall plays only a secondary role in the Gram stain reactions. However, the cell wall of Gram-positive bacteria is indeed...