Cell Wall of Bacteria

The bacterial cell wall is composed of saccharides known as peptidoglycan, although its structure differs between bacterial types. Depending on cell wall structure, bacteria are classified into two main groups: Gram-positive bacteria (e.g. *Bacillus subtilis*) and Gram-negative bacteria (e.g., *Escherichia coli*). This distinction was first identified in 1884 by Christian Gram. Gram-positive bacteria have cell walls primarily consisting of a thick layer of peptidoglycan, which binds strongly to purple dyes, such as crystal violet. This results in a stable coloration. In contrast, Gram-negative bacteria possess only a thin peptidoglycan layer, which is overlaid by an additional membrane with pores. This structure binds the violet dye weakly, allowing it to be washed away with alcohol and replaced by a different stain, typically red (such as safranin). Thus, after Gram staining, Gram-positive bacteria appear purple, while Gram-negative bacteria appear red. The structural differences in bacterial cell walls impact them more than staining outcomes; they are crucial in fields such as medicine. For example, the type of bacterial cell wall plays a significant role in determining which antibiotics are effective for treatment.