Final answer:
Cholera bacteria produce toxins that cause an increase in chloride ion secretion in the intestines, leading to water following the ions, resulting in rapid dehydration and watery faeces known as 'rice water stool'.
Step-by-step explanation:
Cholera bacteria, known as Vibrio cholerae, cause severe diarrhoea by producing toxins that lead to an increase in secretion of chloride ions into the lumen of the intestine. This occurs as the cholera toxin activates an intracellular G protein within epithelial cells, leading to the upregulation of adenylate cyclase, which elevates cyclic AMP levels.
The elevated cyclic AMP activates chloride channels, causing the efflux of chloride ions into the intestinal lumen. In response to the increased osmotic pressure, water follows the chloride ions into the lumen, resulting in the watery faeces characteristic of cholera, often referred to as "rice water stool."
This loss of fluids and electrolytes leads to rapid dehydration and electrolyte imbalance, which can be fatal without prompt treatment.