Contrast endotoxins and exotoxins; provide a representative organism for each.

• A. Endotoxins are components of Gram-negative outer membranes (LPS); Exotoxins are secreted proteins; endotoxin example: E. coli LPS; exotoxin example: cholera toxin from Vibrio cholerae.
• B. Endotoxins are secreted proteins; Exotoxins are cell wall components; endotoxin example: Staph aureus toxins; exotoxin example: Penicillin.
• C. Endotoxins are DNA-binding proteins; Exotoxins are RNA-binding; endotoxin example: Bacillus anthracis; exotoxin example: Diphtheria toxin.
• D. Endotoxins are produced by Gram-positive bacteria; Exotoxins are produced by viruses; endotoxin example: Streptococcus; exotoxin example: Herpes toxin.

Answer: (A)

Endotoxins are structural components of the Gram-negative outer membrane, specifically the lipopolysaccharide (LPS) layer. They aren’t secreted toxins; they’re released mainly when the bacterial cell dies or is lysed. Exotoxins, on the other hand, are proteins actively secreted by bacteria into the surrounding environment and can act at very low concentrations with highly specific targets in host cells. This distinction is illustrated by representative examples: an endotoxin is the LPS component of Escherichia coli, while an exotoxin is cholera toxin produced by Vibrio cholerae, which disrupts ion transport in intestinal cells. The other options mix up where endotoxins or exotoxins come from or give incorrect examples (for instance, treating exotoxins as cell wall components or naming non-toxin substances), which doesn’t fit how these toxins operate.