Mycobacterium tuberculosis vs. Mycobacterium avium complex: A comparison

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MTB and MAC are diseases caused by mycobacteria but differ in several ways.

M. tuberculosis causes TB and is a highly contagious respiratory infection, primarily affecting the lungs. Some symptoms of TB include:

• a persistent cough
• fever
• night sweats
• weight loss
• fatigue

In contrast, the MAC consists of several nontuberculous mycobacterial species, known as nontuberculous mycobacteria (NTM). The most prevalent species are M. avium and M. intracellulare. These species commonly exist in the water and soil.

MAC does not cause TB. The infections often target individuals with weakened immune systems or underlying lung conditions. Therefore, doctors consider it an opportunistic bacteria.

Furthermore, the MAC can affect various body systems, including:

• lungs
• lymph nodes
• skin
• other organs

Symptoms can vary depending on the site of infection. Doctors refer to these as nontuberculous mycobacterial (NTM) diseases.

MTB and MAC tend to share some characteristics, including:

• Shape: Both species are rod-shaped.
• Slow-growing: Both may take several weeks before they cause symptoms.
• Non-spore forming: Both may remain dormant and cause infection when under stress.
• Aerobic: Both require oxygen to survive.

There are key differences in some of the characteristics of M. tuberculosis and MAC species.

M. tuberculosis has a unique cell wall structure composed of mycolic acids, contributing to its potential to become resistant to certain antibiotics. This can make treating TB difficult.

The MAC is a group of closely related mycobacterial species that share similar characteristics and cause similar infections. The genomes of MAC species are large, containing thousands of genes involved in various cellular processes and adaptations to different environments.

Also, MAC bacteria are environmental organisms commonly found in soil, dust, water sources, and in domestic and wild animals. They have adapted to survive in various conditions.

TB spreads from person to person and can affect anyone. A person acquires TB by inhaling respiratory droplets from another person with active TB. These droplets contain the bacteria, allowing the infection to spread when individuals breathe them in.

In contrast, MAC spreads through environmental exposure to the bacteria. The MAC has been found in Europe, Asia, and the Americas. Infections usually occur because of compromised immune systems, such as those with AIDS, chronic lung diseases, or other factors.

Doctors take different approaches when treating TB and the MAC.

The standard treatment for active TB consists of a combination of several antibiotics for 6–9 months. First-line drugs include:

• isoniazid
• rifampin
• pyrazinamide

Drug resistance is a concern because treatment may not always be effective. Therefore, a typical course may require additional medications and a longer duration if drug-resistant strains are causing infection.

Similarly, doctors often find MAC infections challenging to treat due to the inherent resistance of the bacteria to many commonly used antibiotics. They may prescribe double or triple therapy with macrolide or aminoglycoside antibiotics.

Duration

Treatment duration for MAC infections is generally longer, and a doctor only considers a person cured once samples show no sign of disease for at least 12 months. Therefore, close monitoring and regular follow-ups with healthcare providers are crucial to ensure effective treatment outcomes.

Differentiating between TB and MAC infections requires a comprehensive diagnostic approach. It involves various tests and clinical evaluations. Doctors consider several factors, including a person’s medical history, symptoms, and risk factors, to diagnose accurately.

Tests

There are two main tests to detect TB infection:

• TB skin test (TST):
  • Involves injecting some tuberculin — a sterile solution derived from M. tuberculosis — into the skin.
  • A positive result indicates exposure to TB, but doctors need further evaluation for diagnosis.
  • This test may not be helpful to diagnose active TB disease.
• TB blood test (IGRAs):
  • Involves drawing blood and measuring the immune response, specifically through the release of a substance called interferon-gamma.
  • A positive blood test, where a reaction occurs, means a person has the bacteria.
  • This test provides a more rapid diagnosis compared to the TST and may be beneficial to those with the Bacille Calmette-Guérin (BCG) vaccination.
  • However, doctors must further evaluate the person to determine the infection status.

Learn more about the BCG vaccine.

When combined with other tests, such as imaging tests or other diagnostic examinations, the TB skin and blood tests can help healthcare providers determine the presence of TB infection and guide appropriate management.

When considering MAC infections, doctors make a clinical assessment and may use imaging tests. Laboratory testing is also beneficial. It involves collecting samples, such as blood, sputum, or tissue samples, from the affected site and performing cultures or molecular tests to identify the disease-causing species.

Mycobacterium tuberculosis and Mycobacterium avium complex (MAC) are bacteria that cause different infections. Both belong to the genus Mycobacteria. M. tuberculosis causes TB, which primarily spreads through the inhalation of infected respiratory droplets.

In contrast, the MAC consists of several related bacterial species, including Mycobacterium avium and Mycobacterium intracellulare. Typically, infections occur when people with compromised immune systems or underlying lung conditions come into contact with contaminated water, soil, or food.

Understanding the differences between these infections is essential for accurate diagnosis, appropriate treatment, and effective prevention strategies. By addressing these infections promptly and comprehensively, doctors can mitigate their impact on individuals and communities.