Cengage Microbiology Practice Test

Endotoxins are components of the outer membrane of Gram-negative bacteria, with the toxic signal coming from lipid A within lipopolysaccharide. The lipid A portion triggers a strong inflammatory response through TLR4, which is why lipopolysaccharide is the classic endotoxin. The other molecules are not endotoxins: teichoic acid and lipoteichoic acid are features of Gram-positive cell walls, and peptidoglycan is the structural polymer giving rigidity to bacterial walls. LPS, containing lipid A, is the endotoxin.