Which type of bacteria often presents a more complex cell wall?

Gram-negative bacteria are known for their complex cell wall structure, which consists of a thin peptidoglycan layer surrounded by an outer membrane. This outer membrane contains lipopolysaccharides and provides an additional barrier that can make Gram-negative bacteria more resistant to certain antibiotics and substances that can easily penetrate the cell walls of Gram-positive bacteria.

The structure of Gram-negative bacteria allows for greater variability in their cell wall composition, including the presence of porins that facilitate the transport of molecules, as well as the ability to evade the immune response. Mycobacteria, while also notable for their complex cell wall due to the presence of mycolic acids, are classified separately due to their distinct characteristics and staining properties. Gram-positive bacteria typically have a simpler structure with a thick peptidoglycan layer and lack the outer membrane found in Gram-negative bacteria. Spore-forming bacteria, while they have unique features such as the ability to form spores under adverse conditions, do not necessarily have a more complex cell wall compared to Gram-negative bacteria. Thus, among the choices provided, Gram-negative bacteria are correctly identified as having the more complex cell wall.