Endotoxin Myths Busted: What’s Not True About Bacterial Toxins

Endotoxins, or lipopolysaccharides (LPS) from Gram-negative bacteria, are heat-stable but only weakly immunogenic, contrary to common misconceptions. This MCQ clarifies endotoxin properties for microbiology students preparing for exams like NEET or CSIR NET.

Question Breakdown

The question is: “What is not true about endotoxin?” Options: 1. Endotoxin is heat-stable, 2. Endotoxin is strongly immunogenic, 3. Endotoxin is present in gram negative bacteria, 4. Endotoxin is a lipid in nature.​

Correct Answer

2. Endotoxin is strongly immunogenic. Endotoxins (LPS) are weakly immunogenic, requiring carriers for antibody production, unlike strongly immunogenic exotoxins which are proteins.

Option Explanations

Endotoxin is Heat-Stable (Option 1)

True. Endotoxins resist heat up to 250°C for 30 minutes due to their stable Lipid A structure, distinguishing them from heat-labile exotoxins.

Endotoxin is Strongly Immunogenic (Option 2)

False. Endotoxins evoke non-specific inflammation via TLR4 but poor specific antibody responses without adjuvants; exotoxins are highly immunogenic.

Endotoxin is Present in Gram Negative Bacteria (Option 3)

True. LPS forms 75% of the outer membrane in Gram-negative bacteria like E. coli, released upon cell lysis.

Endotoxin is a Lipid in Nature (Option 4)

True. Endotoxins are lipopolysaccharides with hydrophobic Lipid A (phospholipid-like), polysaccharide core, and O-antigen.

Endotoxin vs Exotoxin Table

Endotoxins cause sepsis via innate immunity, key for infection pathology in exams.​