Botulinum toxin is the example of a neurotoxin among the given options.
Neurotoxins specifically target the nervous system, disrupting nerve function such as neurotransmitter release. This multiple-choice question tests knowledge of bacterial toxins and their mechanisms, common in exams on microbiology and biochemistry.

Option Analysis

• (A) Cholera toxin: Produced by Vibrio cholerae, this AB5 enterotoxin binds GM1 gangliosides in the gut, leading to massive cAMP elevation and watery diarrhea. It primarily affects intestinal epithelial cells, not neurons.​

• (B) Streptolysin-O: A cholesterol-binding hemolysin from Streptococcus pyogenes that forms pores in host cell membranes, causing lysis in erythrocytes and other cells. It acts as a cytolysin with immunomodulatory effects but does not target neural tissues.​

• (C) Botulinum toxin: Correct answer. Secreted by Clostridium botulinum, this AB toxin cleaves SNARE proteins (e.g., SNAP-25, VAMP), blocking acetylcholine release at neuromuscular junctions. It causes flaccid paralysis, exemplifying neurotoxicity.​

• (D) Diphtheria toxin: From Corynebacterium diphtheriae, an AB exotoxin that ADP-ribosylates elongation factor-2 (EF-2) in eukaryotes, halting protein synthesis. It primarily damages respiratory epithelium and heart tissue systemically, not nerves directly.​

Introduction: Understanding Neurotoxin Examples

In microbiology and toxicology, identifying a neurotoxin example is crucial for grasping how bacterial toxins disrupt biological systems. A neurotoxin targets neural components like synapses or axons, often blocking neurotransmitter release. Among options like Cholera toxin, Streptolysin-O, Botulinum toxin, and Diphtheria toxin, only one qualifies as a true neurotoxin example.​

Bacterial Toxins Overview

Bacterial toxins fall into categories: exotoxins (secreted proteins) and endotoxins (LPS). Neurotoxins are a subset of exotoxins acting on nerves.

• Cholera toxin: Enterotoxin causing diarrhea via cAMP dysregulation.​

• Streptolysin-O: Pore-forming cytolysin aiding bacterial invasion.​

• Botulinum toxin: Classic neurotoxin example, inhibiting vesicle fusion.​

• Diphtheria toxin: Inhibits translation in many cells.​

Why Botulinum Toxin is the Neurotoxin Example

Botulinum toxin (BoNT) exemplifies neurotoxicity by entering motor neurons and cleaving SNAREs, preventing ACh exocytosis. This leads to paralysis, as seen in botulism. Unlike others, its primary site is the neuromuscular junction.​

Clinical and Research Relevance

BoNT’s medical use (e.g., Botox) highlights its precision, contrasting lethal effects of Cholera or Diphtheria toxins. Streptolysin-O contributes to streptococcal diseases but lacks neural specificity.​