Tuberculosis (TB) is a bacterial infection caused by a germ called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but they can also damage other parts of the body. TB spreads through the air when a person with TB of the lungs or throat coughs, sneezes or talks. If you have been exposed, you should go to your doctor for tests. You are more likely to get TB if you have a weak immune system.

Symptoms of TB in the lungs may include

A bad cough that lasts 3 weeks or longer
Weight loss
Coughing up blood or mucus
Weakness or fatigue
Fever and chills
Night sweats
If not treated properly, TB can be deadly. You can usually cure active TB by taking several medicines for a long period of time. People with latent TB can take medicine so that they do not develop active TB.

In the blue image below, pink rod like structures are the tubercle bacilli; first isolated by Robert Koch.

And on histopathology large pink area is that of typical necrosis caseation type of necrosis and on the right we have tuberculoid granulomas with giant cells.