AS Biology: Cholera

How the vibrio cholerae causes cholera and the symptoms.

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  • Created by: Lexi
  • Created on: 08-05-12 19:08


Structure of bacteria:

  • Capsule of mucilaginous slime- protects the bacterium from any mechanical attack, helps groups of bacteria to stick together
  • Cell wall made of peptidoglycan- for support and acts as a barrier
  • Plasma membrane- partially permeable, controls the enrty and exit of materials
  • Plasmids- contains the genes for survival against adverse conditions, eg gene for antibiotic resistance. These can be transferred between bacteria
  • Circular DNA- long and coiled, floating freely in the cell. Contains genetic material in the form of circular DNA
  • Flagella- long, thin 'tail' or extension of the cell. Rigid, corkscrew shape. Aids movement through fluid when it rotates

It is this structure which helps its success. It is fairly small and simple in its structure.

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Causing Cholera

Cholera is transmitted by drinking water or eating food that has been contaminated by faecal material containing the pathogen. (Vibrio Cholerae)

  • Almost all the bacteria ingested in killed by the acidic conditions in the body, however some survive, especially if the pH is above 4.5
  • It uses its flagella to propel itself through the mucus lining of the intestinal wall
  • It then produces a toxin which has two parts. The first binds to carbohydrate receptors on the cell-surface membrane. The second enters the epithelial cells causing the chloride ion channels to open
  • This causes chloride ions to flood out of the cells and into the lumen of the intestine, raising the water potential of the cells and lowering the WP of the lumen
  • Water then moves out of the epithelial cells and into the lumen of the intestine
  • The loss of ions from the cells establishes a concentration gradient, causing ions from the blood and surrounding tissues to diffuse into the cells
  • Resulting in a movement of water by osmosis from the tissues and blood (as they now have a high WP) into the intestine
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Oral Rehydration Therapy

Giving those suffering from cholera water is ineffective for two reasons:

  • Water is not being absorbed from the intestines. Its remaining in there and passing out in diarrhoea
  • Water does not replace the lost electrolytes/ions

In order for the ORT to work, it must use alternative protein carrier in the cell-surface membranes of the epithelial cells. As the sodium ions are absorbed, the WP of the cells will fall; causing water to be absorbed via osmosis.

The ORS needs to contain:

  • Water: to rehydrate the tissues
  • Glucose: provide a source of energy + stimulate the uptake of sodium ions
  • Sodium: make optimum use of the sodium-glucose carrier proteins + replace the lost sodium ions
  • Potassium: stimulate appetite + replace lost potassium ions
  • Other electrolytes: prevent electrolyte imbalances
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