What is an endotoxin?

An endotoxin is specifically defined as a toxin that is a structural component of the bacterial cell wall, particularly from gram-negative bacteria. The primary example of an endotoxin is lipopolysaccharide (LPS), which is found in the outer membrane of gram-negative bacteria. When these bacteria are lysed or die, they release endotoxins into the surrounding environment. Endotoxins are known to trigger significant immune responses in humans and other animals, leading to symptoms such as fever, inflammation, and septic shock in severe cases.

In contrast, toxins produced by fungi do not fit the definition of an endotoxin; rather, they are classified differently, and the term 'toxin' in that context typically describes secondary metabolites rather than structural components. Options related to natural defenses and viral particles are unrelated to the specifics of endotoxin, as they do not involve bacterial cell structure or function. Hence, the selection of the correct definition aligns accurately with the established characteristics of endotoxins in microbiology.