Bacterial Cell Wall

The bacterial cell wall is a rigid structure surrounding the plasma membrane. It maintains the cell's shape and protects it from osmotic pressure.

It is composed of peptidoglycan, a polymer of alternating sugars—N-acetylglucosamine and N-acetylmuramic acid—linked by amino acids, forming a flexible mesh.

Gram-positive bacteria have thick peptidoglycan layers.

They also contain teichoic acids, which facilitate ion uptake and protect cells from harmful substances and host defense molecules.

Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane with lipopolysaccharides, which have endotoxin activity that triggers the host’s immune response and provides structural integrity.

The Gram stain distinguishes bacteria by cell wall structure. Gram-positive bacteria appear purple as they retain the crystal violet dye, while Gram-negative bacteria appear pink due to a counterstain.

The composition of the cell wall also determines susceptibility to antibiotics. For example, Gram-positive bacteria are more susceptible to penicillin than Gram-negative bacteria.