Yes, tuberculosis is caused by a bacterium

Tuberculosis (TB) is caused by a bacterium called Mycobacterium tuberculosis. This is a living microorganism—a single-celled creature so small you cannot see it without a microscope. When a person with TB coughs, sneezes, or speaks, they release droplets containing this bacterium into the air. Another person can breathe in these droplets and become infected.

The bacterium settles in the lungs and begins to multiply. This is why TB is often called a lung disease, though the bacteria can spread to other parts of the body. The infection develops slowly—some people never develop symptoms at all, while others become sick weeks or months after breathing in the bacterium.

Key Takeaways

  • Mycobacterium tuberculosis is a bacterium, not a virus or fungus, and it spreads through the air when an infected person coughs or sneezes.
  • The bacterium has a thick, waxy outer coating that makes it harder to kill than many other bacteria, which is why TB treatment requires multiple antibiotics taken for months.
  • Not everyone infected with TB becomes sick—some people carry the bacterium without symptoms, a condition called latent TB infection.
  • TB is treatable with antibiotics, but the bacterium can develop resistance if medications are not taken exactly as prescribed.

How the tuberculosis bacterium spreads

Mycobacterium tuberculosis spreads from person to person through the air. When someone with active TB disease coughs, sneezes, speaks, or sings, they release tiny droplets containing the bacterium. A nearby person can breathe these droplets in and become infected.

You cannot catch TB from shaking hands, sharing food or drink, or touching someone's skin. The bacterium must reach the lungs, which is why close contact with someone who has active TB—such as living in the same household or working in the same room for hours—carries the highest risk. People with latent TB infection (the bacterium present but no symptoms) do not spread the disease.

Why this bacterium is difficult to treat

Mycobacterium tuberculosis has a thick, waxy outer coating that protects it from many antibiotics and from the body's immune system. This coating makes the bacterium harder to kill than most other bacteria. Because of this, TB treatment requires multiple antibiotics taken together for at least six months—not just one or two weeks of medication.

If someone stops taking their TB medications early, even if they feel better, the remaining bacteria can survive and develop resistance to the drugs. Drug-resistant TB is much harder to treat and requires longer courses of different antibiotics. This is why doctors emphasize finishing the entire course of treatment, even after symptoms disappear.

The difference between latent and active TB infection

When a person first breathes in Mycobacterium tuberculosis, they become infected. However, infection does not always mean disease. The body's immune system can contain the bacterium, keeping it dormant (inactive) in the lungs. This is called latent TB infection. A person with latent TB has no symptoms, does not feel sick, and cannot spread TB to others.

In some people—particularly those with weakened immune systems, young children, or older adults—the bacterium breaks through the immune system's defenses and begins to multiply actively. This causes active TB disease, with symptoms like cough, fever, and chest pain. Only people with active disease can spread TB to others. A doctor can determine whether someone has latent or active TB using a skin test, blood test, or chest X-ray.

How doctors identify TB bacteria

Doctors use several methods to detect Mycobacterium tuberculosis. The most common are a tuberculin skin test (also called a Mantoux test), where a small amount of TB protein is injected under the skin and checked for a reaction after 48 to 72 hours, and blood tests that look for the body's immune response to TB.

To confirm active TB disease, a doctor may order a chest X-ray to look for signs of infection in the lungs, or a sputum smear test, where a sample of mucus coughed up from the lungs is examined under a microscope for TB bacteria. A culture test, which grows the bacterium in a laboratory over several weeks, can also identify TB and test which antibiotics will work against it.

Treatment with antibiotics

Because Mycobacterium tuberculosis is a bacterium, it can be treated with antibiotics. The standard treatment for active TB involves taking four antibiotics together for two months, followed by two antibiotics for four more months. The exact medications and length of treatment may vary depending on the type of TB and whether the bacterium is resistant to certain drugs.

Taking medications exactly as prescribed is critical. Missing doses or stopping early allows the bacterium to survive and can lead to treatment failure or drug resistance. Many people receive directly observed therapy (DOT), where a health worker watches them take each dose to ensure they complete treatment. With proper treatment, most people with TB are cured.

Frequently Asked Questions

Can you catch TB from someone who is taking antibiotics?

A person with active TB can spread the disease to others for about two weeks after starting antibiotics, though the risk drops significantly after that. Once someone has been on TB medication for two to three weeks and shows improvement, they are generally no longer contagious. Your doctor will tell you when it is safe to return to work or school.

Is TB the same as a cold or flu?

No. A cold or flu is caused by a virus, while TB is caused by a bacterium. This means antibiotics do not treat colds or flu, but they do treat TB. TB symptoms also develop more slowly and last much longer than cold or flu symptoms.

What happens if TB bacteria become resistant to antibiotics?

Drug-resistant TB occurs when the bacterium survives antibiotics because treatment was incomplete or incorrect. It requires longer treatment with different, stronger medications that often have more side effects. This is why finishing your full course of TB treatment, even after you feel better, is so important.

Can you be immune to TB after you recover?

Recovery from TB does not may provide immunity. A person who has been treated for active TB can become infected again if exposed to the bacterium. However, people who have had TB are at higher risk of developing active disease again if their immune system weakens.