ekzotoksin

Ekzotoksin, commonly called exotoxin in English, refers to a toxin that is secreted by certain microorganisms, most notably bacteria, into the surrounding environment or into a host during infection. Exotoxins are usually proteins or glycoproteins and are often released actively by living cells, though some are released upon cell lysis. They are typically highly potent and can act at very low concentrations on specific targets such as nerves, muscles, or signaling pathways. Exotoxins differ from endotoxins, which are components of the outer membrane of some bacteria (such as lipopolysaccharides in Gram-negative bacteria) and are released mainly when bacteria die.

Exotoxins are typically classified by their mechanism of action. AB toxins are a common subclass, containing an enzymatically active A subunit and a binding B subunit that targets the toxin to a specific cell. Examples include diphtheria toxin (inhibits protein synthesis by modifying elongation factor-2), botulinum and tetanus toxins (neurotoxins that disrupt neurotransmitter release), and cholera toxin (overactivates adenylate cyclase leading to watery diarrhea). Non-AB exotoxins include membrane-disrupting toxins (pore-forming toxins) and superantigens that trigger excessive immune responses, such as some Staphylococcus aureus toxins.

Clinically, exotoxins drive the symptoms and severity of diseases such as diphtheria, botulism, tetanus, and cholera. Because exotoxins are highly immunogenic, many have been inactivated to form toxoids for vaccines (for example, diphtheria and tetanus vaccines). Some exotoxins, like botulinum toxin, have therapeutic and cosmetic applications at controlled doses.

In summary, ekzotoksin denotes a potent, secreted toxin produced by bacteria that disrupts specific host processes, distinct from endotoxins that are part of the bacterial cell wall.