Surrounding the bacterial plasma membrane is a cell wall composed of peptidoglycan. Peptidoglycan is composed of two glucose derivatives (N-acetylmuramic acid and N-acetylglucosamine) that are joined together into long chains. These long carbohydrate chains are then joined together by short amino acid chains, and the entire molecule is stabilized by additional peptide chains.

The cell wall has a number of functions, including maintaining the shape of the cell, preventing the rupture of the cell in response to osmotic stress, and in some cases, contributing to the virulence of a bacterium. Antibiotics such as penicillin are effective because they disrupt the synthesis of peptidoglycan, thereby making the bacterium more susceptible to osmotic stress. Some bacteria, referred to as gram-negative bacteria, possess an additional outer membrane that surrounds the cell wall.

A few groups of bacteria are able to produce structures referred to as endospores in times of nutritional stress. These endospores are difficult to kill and will remain dormant until introduced into an environment that is nutrient rich. Some examples of bacteria that produce these structures are Clostridium tetani (the causative agent of tetanus) and Bacillus anthracis, the causative agent of anthrax.