Those bacteria which takes place gram stain made up of Crystal violet and Iodine are called gram positive (+) bacteria and those bacteria does not colored by gram stain are called gram negative (-) bacteria. The gram staining method was first used by the scientist Cristian Gram of Denmark in the year 1884.
Examples of two gram positive and two gram negative bacteria.
Names of two gram positive bacteria- Bacillus subtilis, Staphylococcus aureus.
Names of two gram negative bacteria- Escherichia coli, Salmonella aureus.