Which type of toxin is a structural component of bacteria?

Endotoxins are indeed structural components of bacteria, specifically found in the outer membrane of Gram-negative bacteria. Unlike exotoxins, which are actively secreted by living bacteria and can be proteins or enzymes, endotoxins are released when the bacterial cells are damaged or lysed. The main component of endotoxins is lipopolysaccharide (LPS), which plays a crucial role in the structural integrity of the bacterial cell wall and can elicit strong immune responses in the host. This distinction underscores the fundamental difference between endotoxins and the other types of toxins listed.

The other options refer to different categories of toxins that either do not serve as structural components of bacteria or are not directly related to the bacterial cell structure. Understanding the role of endotoxins provides insight into bacterial pathogenesis and the immune responses they trigger.