Exotoxins

Definition

Potent, soluble proteins secreted by living bacteria that cause direct damage to host cells or disrupt normal cellular metabolism, distinguishing them from endotoxins which are structural components of the bacterial cell wall released upon cell lysis. Exotoxins may act locally at the site of infection or be transported systemically to target specific tissues or organ systems.

Etymology

Greek exo- (outside) + toxikon (arrow poison, toxin), referring to their secretion outside the bacterial cell

Example

The bacterium Bacillus thuringiensis produces crystalline protoxins that, when ingested by lepidopteran larvae, are solubilized in the alkaline midgut and processed into active exotoxins that disrupt epithelial integrity, causing gut paralysis and death—this mechanism underlies the widespread use of Bt as a biological insecticide.

Synonyms

• extracellular toxins

Related Terms

• Endotoxins
• enterotoxins
• neurotoxins
• cytotoxins
• virulence factors
• Pathogenicity
• bacterial toxins
• membrane vesicles
• septicemia
• toxemia

Usage Notes

Exotoxins are distinguished from endotoxins by their protein composition, heat lability, and secretion by living cells rather than release from lysed cells. In arthropod-borne disease contexts, exotoxin-mediated pathology may occur secondary to vector transmission (e.g., Clostridium botulinum toxin in wound myiasis, or staphylococcal toxins in secondary infections of tick bite lesions). Some entomopathogenic bacteria deploy exotoxins as virulence factors against insect hosts. The term is sometimes loosely applied to secreted fungal toxins, though purists reserve it for bacterial products.