Choolera Toxin

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4. The mechanism of action of cholera toxin

The cholera toxin is an enterotoxin which is secreted by the gram-negative bacteria Vibrio cholerae. The toxin is an protein complex which is made up by six subunits, one A subunit and five B subunits. The A subunit is the enzymatic subunit and the B subunit is the binding subunit [9]. The cholera toxin is released from the bacteria and once in the intestinal lumen it adheres to the apical surface of the epithelial cell. The B subunit of the toxin binds to a ganglioside receptor, GM1 on the apical surface of the epithelial cell. This triggers endocytosis of the toxin to enable the enzymatic subunit A1 to be released. The A1 subunit enters the epithelial cell cytosol and activates Gsα subunit
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It is also characterised by increased frequency and fluidity [13]. The World Health Organisation (WHO) defines it as the passage of three or more loose or liquid stools per day [14]. There are a number of different types of diarrhoea such as secretory, osmotic, exudative, inflammatory and dysentery [Table 1.]. Overall, diarrhoea results when there is an increase in secretion or reduced absorption from the small intestine enterocyte cells.

Table 1. The different types of diarrhoea, their characteristics and causes [15,16].

6. The causes of diarrhoea

Diarrhoea is usually a symptom of an underlying condition. It can be caused by a number of factors such as [17]:

Gastroenteritis - this is typically acquired from food or water that has been contaminated by faeces or directly from another infected person. This causes infectious diarrhoea and the infectious agents can be bacteria, viruses or parasites. Common causative bacterial agents are Escherichia coli, Vibrio cholerae, Shigella dysenteriae and Clostridium difficile.
Food allergies or food intolerance such as lactose intolerance.
An adverse reaction to medication such as penicillin, antacids and laxatives.
Intestinal malabsorption disorders such as coeliac disease.
Inflammatory conditions of the intestinal tract such as Ulcerative colitis or Crohn’s disease which can lead to chronic

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