Tuberculosis general caused by Mycobacterium tuberculo­sis about diagnosis classification of Tuberculosis

Tuberculosis general caused by Mycobacterium tuberculo­sis

Tuberculosis is caused by Mycobacterium tuberculo­sis.

The disease affects the lungs and other organs. It is a curable disease, if treated.

If not treated, then death can occur in about 5 years. Transmission is through air-borne droplet nuclei pro­duced by patients of infectious pulmonary tuberculo­sis.

Mycobacterium tuberculosis


Causative agents of Tuberculosis — 

  • Mycobacterium tuberculosis
  • Mycobacterium bovis (Bovine tubercle bacillus transmitted by unpasteurised milk)
  • Mycobacterium africanum (Isolated from Africa)
  • Mycobacterium microti (Rare)
  • M. canettii (Rare)

M. tuberculosis is rod-shaped, non-spore-forming, aerobic bacteria, neutral on gram staining.

The bacilli are acid-fast bacilli due to high content of mycolic acids and other cell wall lipids.

The risk of developing tuberculosis after infection with M. tuberculosis depends on the host susceptibility and immunity.

Atypical or non-tuberculous mycobacteria (NTM) are  —

  • M. avium
  • M.intracellular
  • M. kansaii
  • M. marinum
Pathogenesis and immunity
  • The NTM are also calLed environmental mycobacte­ria. They are less virulent for humans than M. tuber­culosis. They can cause pulmonary disease and lym­phadenitis.

Primary tuberculosis –

  • If disease occurs directly after infection,
  • it is called primary tuberculosis.
  • It is common in children.
  • Primary tuberculosis may be severe, disseminated, but not transmissible.

Tuberculosis develops within 1 or 2 years after infec­tion, but bacilli may persist for many years.

Secondary tuberculosis

  • When old bacteria be­come reactivated to cause disease, it is called sec­ondary tuberculosis.
  • Secondary or post primar tuberculosis is infectious.
  • The risk of M. tuberculosis is very high in HIV infected persons.
Pathogenesis and immunity


  • Age for common Tuberculosis
  • Common in adolescents to adult. Tuberculosis is also common in elderly.

Predisposing factors

  • Tubercul osis is common in patients of HIV,
  • patients with low immunity, silicosis,
  • CRF(chronic renal failure), patientson hemodial sis,
  • diabetes, IV drug usecs.,
  • patients with astrectom patients of renal and cardiac transplant, malnutrition .


Pathogenesis and immunity

  • Inhaled bacilli are cleared by upper airway but some reach the alveoli.
  • Some genes make the bacilli virulent like: kat G and rpo V.
  • Genetic factors are also important in resistance to infection. Delayed type hypersensitivity reaction gives rise to tissue damaging response.
  • Cell mediated immunity, and humoral immunity are less important.
  • Tuberculosis may be pulmonary or extra-pulmonary. In HIV patients both extra-pulmonary and pulmonary occur together.



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