Which component is primarily responsible for the outer membrane of Gram-negative bacteria and contributes to endotoxin activity?

• A. Teichoic acids
• B. Lipopolysaccharide
• C. Peptidoglycan
• D. Capsule

Answer: (B)

Gram-negative bacteria have an outer membrane whose distinctive component is lipopolysaccharide. This molecule anchors in the outer membrane and includes lipid A, the part that functions as the endotoxin, provoking strong inflammatory responses when released. The O-antigen and core polysaccharide extend outward and influence antigenicity and membrane stability, but the endotoxin activity comes from lipid A within LPS. Teichoic acids belong to Gram-positive cell walls and are not part of the outer membrane or endotoxins. Peptidoglycan forms the structural mesh of the cell wall, not the outer membrane, and capsules are extra-polysaccharide layers outside the wall that affect virulence but aren’t responsible for outer-membrane endotoxin activity.