Tuberculosis is an infectious disease caused by the bacterial species named Mycobacterium Tuberculosis.

An individual obtains the infection by breathing in Mycobacterium Tuberculosis bacteria, which are aerosolised when an individual with the infection coughs. Once in the lung tissue it is very difficult for the human immune system to destroy the bacteria and instead what usually happens is it sets off a chronic battle between the immune system and the bacteria, in which neither wins and instead the bacteria just remain contained within a small granuloma of inflammatory cells within the lungs. This is known as latent tuberculosis.

Whilst the individual remains strong and healthy, the immune system will continue this battle and continue to successfully contain the mycobacteria. However if a period of significant illness befalls the individual then the strength of their immune system may be compromised temporarily. Alternatively if they develop AIDs or are placed on immunosuppressants or chemotherapy these also would result in immunological compromise.

Immunological compromise can then lead to the immune system no longer being able to sufficiently continue this fight with the mycobacteria. Control over the mycobacterial population would be lost and they would successfully raise their numbers. As their numbers grow they would spread into the surrounding lung tissue and destroy it and if the immune system doesn’t get it back under control quickly the expansion will continue and a full blown worsening TB infection would have begun.

The bacteria can spread from the site of infection in the lungs into the circulation and disseminate around the body. They can hence set up foci of infection all over the body. This is called miliary tuberculosis. If the infection is not brought under control then it will gradually destroy more and more of the body’s tissue and organ failure of the affected organs will follow.

In this video I describe and explain the pathogenesis of tuberculosis and the granulomatous inflammatory response produced to it. In the final part of the video we look at the pharmacological mechanisms of the antibiotics used to treat it, namely rifampicin, isoniazid, pyrazinamide and ethambutol.

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