Introduction
Mycobacterium tuberculosis is the bacterium that causes tuberculosis, commonly called TB. It is the main causative organism of human tuberculosis and is one of the most important disease-causing bacteria in public health.
Nature of the organism
It is a:
• bacterium
• rod-shaped organism
• aerobic organism, meaning it prefers oxygen-rich environments
• slow-growing pathogen
Because it grows slowly, diagnosis and treatment monitoring can be more difficult compared to many other bacteria.
Disease caused
Mycobacterium tuberculosis causes tuberculosis.
It mainly affects:
• lungs, causing pulmonary tuberculosis
• lymph nodes
• bones
• kidneys
• brain and meninges
• other organs in severe or disseminated forms
So, TB is not only a lung disease. It can affect multiple organs.
Transmission
The bacterium spreads mainly through the air.
When a person with active pulmonary TB coughs, sneezes, or speaks, tiny infected droplets may enter the air and be inhaled by others.
Thus, tuberculosis is an airborne infectious disease.
Special feature
One of the most important features of Mycobacterium tuberculosis is that it has a waxy cell wall rich in mycolic acid.
This gives it important properties:
• resistance to drying
• difficulty in staining by ordinary methods
• acid-fast nature
That is why it is called an acid-fast bacillus.
Acid-fast property
Mycobacterium tuberculosis is classified as an acid-fast bacillus because it retains certain stains even after treatment with acid-alcohol.
This is why Ziehl–Neelsen staining is commonly associated with TB diagnosis.
Growth characteristics
It is a slow-growing organism. Colonies may take weeks to appear in culture.
This slow growth is important because:
• diagnosis can be delayed
• treatment has to be prolonged
• the organism can persist in the body for long periods
Latent and active infection
Mycobacterium tuberculosis can remain in the body in two important forms:
Latent TB infection
In this stage, the bacterium remains in the body but does not produce active disease symptoms. The person is infected but not usually infectious.
Active TB disease
In this stage, the bacteria multiply and cause symptoms such as cough, fever, weight loss, and night sweats. This stage is clinically important because it can spread to others.
Pathogenesis
After entering the lungs, the bacteria are taken up by macrophages. However, Mycobacterium tuberculosis can survive inside these cells and trigger a prolonged immune response.
This leads to the formation of granulomas, which are characteristic in TB.
Symptoms of tuberculosis caused by this bacterium
Common symptoms include:
• chronic cough
• fever
• night sweats
• weight loss
• weakness
• sometimes blood in sputum
Diagnosis
Diagnosis of infection caused by Mycobacterium tuberculosis may involve:
• sputum examination
• acid-fast staining
• culture
• molecular tests such as NAAT
• chest X-ray
• tuberculin skin test or IGRA for latent infection
Drug resistance
A major problem with Mycobacterium tuberculosis is that some strains have developed drug resistance.
Important forms include:
• multidrug-resistant TB
• extensively drug-resistant TB
This makes treatment more difficult and is a major global health challenge.
Importance in public health
Mycobacterium tuberculosis is extremely important because:
• it causes a major infectious disease burden
• it spreads through air
• it may remain latent for years
• drug resistance is increasing
• it needs long treatment duration
Difference from other mycobacteria
Mycobacterium tuberculosis belongs to the genus Mycobacterium, which also includes other species.
For example:
• Mycobacterium leprae causes leprosy
• Mycobacterium tuberculosis causes tuberculosis
Conclusion
Mycobacterium tuberculosis is the bacterium responsible for tuberculosis. It is a slow-growing, acid-fast, aerobic bacillus with a mycolic-acid-rich cell wall. It mainly affects the lungs but can spread to many organs, making it one of the most important pathogens in medicine and public health.
