What structure is commonly found in Gram-negative bacteria's cell wall?

In Gram-negative bacteria, the cell wall is characterized by the presence of an outer membrane, which is a defining feature that distinguishes them from Gram-positive bacteria. This outer membrane is composed of a phospholipid bilayer containing proteins known as porins, as well as lipopolysaccharides (LPS), which play a crucial role in protecting the bacterium from the host's immune system and antibiotics. The outer membrane serves to enhance the permeability barrier of Gram-negative bacteria, allowing them to survive in hostile environments.

The structure of the outer membrane is significant in terms of its impact on the bacterium’s overall physiology and pathogenicity. For example, the lipopolysaccharides on the outer membrane can trigger strong immune responses in the host organism, making these bacteria potentially more virulent.

In contrast, Gram-positive bacteria primarily have a thick peptidoglycan layer and do not possess an outer membrane, which is why the outer membrane is specifically associated with Gram-negative bacteria. Therefore, the presence of the outer membrane is a key component in understanding the differences in cell wall structure between the two classes of bacteria.