Which statement about endotoxins is true?

• A. Endotoxins are proteins that can be converted to toxoids.
• B. Endotoxins are primarily produced by Gram-positive bacteria.
• C. Endotoxins are secreted actively by living bacteria.
• D. Endotoxins are part of the outer membrane of Gram-negative bacteria.

Answer: (D)

Verified step by step guidance

1. Understand what endotoxins are: Endotoxins are lipopolysaccharides (LPS) found in the outer membrane of Gram-negative bacteria, not proteins.
2. Recall the difference between endotoxins and exotoxins: Exotoxins are proteins secreted actively by bacteria and can be converted to toxoids, whereas endotoxins are structural components and are not secreted.
3. Identify the bacterial groups associated with endotoxins: Endotoxins are characteristic of Gram-negative bacteria due to their outer membrane structure, while Gram-positive bacteria lack this outer membrane and do not produce endotoxins.
4. Recognize that endotoxins are released mainly when the bacterial cell dies and the outer membrane breaks apart, rather than being actively secreted by living bacteria.
5. Conclude that the true statement is that endotoxins are part of the outer membrane of Gram-negative bacteria, distinguishing them from exotoxins and their properties.