bacteria are assigned into two separate groups based on the
outcome of a defined bacterial staining procedure, called the Gram staining method;
based on this very common microbiological staining procedure (named after the Danish
physician Ch. Gram who developed this method in 1884), bacteria are classified into:
1. Gram-negative bacteria and
- loose the crystal violet dye after ethanol washing (see panel c. in Image below)
2. Gram-positive bacteria
- retain the crystal violet stain after washing (see panel a. in Image below)