Mycobacterium tuberculosis bacteria

Mycobacterium tuberculosis

mycobacterium tuberculosis mycobacterium tuberculosis animated

Mycobacterium tuberculosis on Löwenstein-Jensen medium after 6 weeks of cultivation, 37°C. Typical nonpigmented, rough, dry colonies on Löwenstein-Jensen medium. The green color of the medium is due to the presence of malachite green which is one of the selective agents to prevent growth of most other contaminants. Unlike many other solid cultivation media used in clinical microbiology Löwenstein-Jensen medium (or e.g., Ogawa medium) doesn't contain any agar (solid consistence is attained by heat coagulation of the egg albumin).

Mycobacterium tuberculosis (MTB) is a pathogenic bacterial species in the genus Mycobacterium and the causative agent of most cases of tuberculosis. First discovered in 1882 by Robert Koch, M. tuberculosis has an unusual, waxy coating on the cell surface (primarily mycolic acid), which makes the cells impervious to Gram staining; acid-fast techniques are used instead. The physiology of M. tuberculosis is highly aerobic and requires high levels of oxygen. Primarily a pathogen of the mammalian respiratory system, MTB infects the lungs, causing tuberculosis.

M. tuberculosis requires oxygen to grow. It does not retain any common bacteriological stain due to high lipid content in its wall, and thus is neither Gram-positive nor Gram-negative; hence Ziehl-Neelsen staining, or acid-fast staining, is used. While Mycobacteria do not seem to fit the Gram-positive category from an empirical standpoint (i.e., they do not retain the crystal violet stain), they are classified as acid-fast Gram-positive bacteria due to their lack of an outer cell membrane.

M. tuberculosis divides every 15-20 hours, which is extremely slow compared to other bacteria, which tend to have division times measured in minutes (Escherichia coli can divide roughly every 20 minutes). Its unusual cell wall, rich in lipids (e.g., mycolic acid), is likely responsible for this resistance and is a key virulence factor. When in the lungs, M. tuberculosis is taken up by alveolar macrophages, but they are unable to digest the bacterium. Its cell wall prevents the fusion of the phagosome with a lysosome. Specifically, M. tuberculosis blocks the bridging molecule, early endosomal autoantigen 1 (EEA1); however, this blockade does not prevent fusion of vesicles filled with nutrients. Consequently, the bacteria multiply unchecked within the macrophage.


M. tuberculosis is grown on a selective medium known as Löwenstein-Jensen medium, which has traditionally been used for this purpose. However, this method is quite slow, as this organism requires 6-8 weeks to grow (growth of isolated colonies in more than 7 days), which delays reporting of results. A faster result can now be obtained using Middlebrook medium or BACTEC.

Abbreviated from Wikipedia

Mycobacterium tuberculosis basic characteristics


  • ** some isoniazid-resistant strains of M.tuberculosis may be negative

Identification of Mycobacterium tuberculosis

  • Slow growing mycobacteria (growth of isolated colonies in more than 7 days)
  • Nonpigmented, rough, dry colonies on Löwenstein-Jensen medium
  • Acid-fast (Ziehl-Neelsen or Kinyoun stain)
  • Nonphotochromogenic
  • The niacin test: positive
  • The nitrate reduction test: positive
  • Growth on TCH (thiophene-2-carboxylic acid hydrazide); 10µg/ml: positive, TCH resistant (unlike M.bovis)
  • Growth on pyrazinamidase agar (PZA); 25µg/ml: negative
  • The arylsulfatase test (3-Day test): negative

Treatment of Mycobacterium tuberculosis

Susceptibility testing at least for INH, RIF, and EMB should be always performed!! Drugs are not used singly!! (Why?)

** In the US only, streptomycin is no longer considered a first line drug by ATS/IDSA/CDC because of high rates of resistance.

Second-line drugs (examples)
The second line drugs are only used to treat disease that is resistant to first line therapy
The standard "short" course treatment for TB is isoniazid (along with pyridoxal phosphate to obviate peripheral neuropathy caused by isoniazid), rifampicin (rifampin in the United States), pyrazinamide, and ethambutol for two months, then isoniazid and rifampicin alone for a further four months. The patient is considered to be free of living bacteria after six months (although there is still a relapse rate of up to 7%).

Mycobacterium tuberculosis on Löwenstein-Jensen medium

mycobacterium tuberculosis colony morphology on L-Jensen medium mycobacterium tuberculosis growth on L÷wenstein-Jensen(L-J) medium m.tuberculosis colonies on L÷wenstein-Jensen medium L-J medium and mycobacterium tuberculosis colony morphology mycobacterium tuberculosis mycobacterium tuberculosis, MT mycobacterium tuberculosis colonies mycobacterium tuberculosis on L-J mycobacterium tuberculosis morphologic characteristics close-up of a Mycobacterium tuberculosis culture mycobacterium tuberculosis culture close-up M.tuberculosis colony close-up mycobacterium tuberculosis close-up M.tuberculosis confluent growth mycobacterium tuberculosis on L÷wenstein-Jensen medium cultivation media for mycobacterium tuberculosis mycobacterium tuberculosis on Ogawa and L÷wenstein-Jensen medium

Mycobacterium tuberculosis cultivation

cultivation of mycobacterium tuberculosis in MB/Bact middlebrook 7H9 broth for MB/Bact

Mycobacterium sp.

mycobacterium fortuitum colonies mycobacterium fortuitum on Ogawa medium mycobacterium vaccae mycobacterium fortuitum, consistence of mycobacteria colonies mycobacterium gordonae mycobacterium kansasii

Acid-fast stain (Ziehl-Neelsen & Kinyoun's stain)

acid-fast stained mycobacterial culture specimen cording in mycobacteria m.tuberculosis ziehl-neelsen stain mycobacterium tuberculosis Z-N stain mycobacterium tuberculosis in sputum, Z-N m.tuberculosis, Koch's bacillus, acid fast rods ziehl-neelsen staining of non-acid-fast bacteria acid-fast and non-acid-fast bacilli, micrograph Kinyoun's stain

Mycobacterium tuberculosis SEM & 3D illustrations

mycobacterium tuberculosis sem mycobacterium tuberculosis, acid-fast rods mycobacterium tuberculosis, acid-fast rods

Useful Links