1. Gram-positive bacteria: These bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain used in the Gram staining procedure. Examples include *Staphylococcus*, *Streptococcus*, *Bacillus*, and *Clostridium*.

2. Gram-negative bacteria: These bacteria have a thinner peptidoglycan layer and an outer membrane composed of lipopolysaccharide (LPS). They do not retain the crystal violet stain and appear pink after counterstaining with safranin. Examples include *Escherichia coli*, *Salmonella*, *Pseudomonas*, and *Neisseria*.