Bacterial Infections: Cholera, TB and Stomach Ulcers

Three bacterial infections

A pathogen is an organism that causes disease. Bacteria are single-celled microorganisms, but only some are pathogenic. Pathogenic bacteria may multiply in the body and damage tissues; some also produce toxins that harm cells.

This lesson compares three bacterial infections. For each one, keep a clear chain in mind:

infection → type of pathogen → main effect

Cholera causes diarrhoea

Cholera is caused by bacteria. Its characteristic symptom is diarrhoea, meaning the frequent passing of loose or watery faeces.

The important association is:

cholera → bacterium → diarrhoea

Diarrhoea is the effect of the infection, not the pathogen itself. Severe diarrhoea also means that the body loses water, although the required identifying symptom here is diarrhoea.

Tuberculosis damages the lungs

Tuberculosis, usually shortened to TB, is also caused by bacteria. TB damages lung tissue, so its specified effect is lung damage. Coughing may occur, but the key association required for this infection is:

tuberculosis → bacterium → lung damage

This distinguishes the disease from cholera: both are bacterial, but they affect different parts of the body and cause different effects.

Helicobacter and stomach ulcers

Bacteria called Helicobacter, commonly Helicobacter pylori, can cause stomach ulcers. An ulcer is a break or sore in the lining of an organ. Here, the bacterium is the pathogen and the stomach ulcer is the resulting damage.

The association is:

Helicobacter bacterium → damage to the stomach lining → stomach ulcer

Do not reverse this relationship: a stomach ulcer is not a microorganism and therefore is not the pathogen.

Comparing the infections

All three examples involve bacterial pathogens, but their effects differ:

A useful way to answer a description question is to state the complete biological link. For example: “Tuberculosis is a bacterial infection that causes lung damage.”