Which statement regarding endotoxins is true?

• A. Endotoxins are secreted actively by living Gram-positive bacteria.
• B. Endotoxins are highly specific in their action on host tissues.
• C. Endotoxins are proteins that can be converted to toxoids for vaccination.
• D. Endotoxins are part of the outer membrane of Gram-negative bacteria.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand what endotoxins are. Endotoxins are components of the outer membrane of Gram-negative bacteria, specifically the lipid A portion of lipopolysaccharides (LPS).
2. Step 2: Recognize that endotoxins are not secreted actively; instead, they are released when the bacterial cell wall breaks down, such as during cell death or lysis.
3. Step 3: Note that endotoxins have a generalized effect on the host, often triggering strong immune responses like fever and inflammation, but they are not highly specific in their action on host tissues.
4. Step 4: Differentiate endotoxins from exotoxins. Exotoxins are proteins secreted by both Gram-positive and Gram-negative bacteria and can often be converted into toxoids for vaccines, whereas endotoxins are lipopolysaccharides and cannot be converted into toxoids.
5. Step 5: Conclude that the true statement is that endotoxins are part of the outer membrane of Gram-negative bacteria, which explains their role and characteristics.