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.