Mycobacterium tuberculosis
![Mycobacterium tuberculosis mycobacterium tuberculosis](bacteria photos/mycobacterium tuberculosis photos/mycobacterium tuberculosis.jpg)
![mycobacterium tuberculosis animated](images/mycobacterium-tuberculosis-bacteria.gif)
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.
Cultivation
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.
Mycobacterium tuberculosis basic characteristics
- ACID-FAST RODS
- NONMOTILE
- NON-SPORE-FORMING
- CATALASE: POSITIVE**
- OXIDASE: NEGATIVE
- AEROBES
** 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?)-
First-line drugs
- Isoniazid (INH)
- Ethambutol (EMB)
- Pyrazinamide (PZA)
- Rifampicin (Rifampin) (RMP/RIF)
- Streptomycin** (SM/STM)
** 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
- amikacin (aminoglycosides)
- kanamycin (aminoglycosides)
- ciprofloxacin (quinolones)
- cycloserine For more visit Wikipedia
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](thumbnails/MYTU/mycobacterium tuberculosis 01.jpg)
![mycobacterium tuberculosis growth on Löwenstein-Jensen(L-J) medium](thumbnails/MYTU/mycobacterium tuberculosis 02.jpg)
![m.tuberculosis colonies on Löwenstein-Jensen medium](thumbnails/MYTU/mycobacterium tuberculosis 04.jpg)
![L-J medium and mycobacterium tuberculosis colony morphology](thumbnails/MYTU/mycobacterium tuberculosis 05.jpg)
![mycobacterium tuberculosis](thumbnails/MYTU/mycobacterium tuberculosis 06.jpg)
![mycobacterium tuberculosis, MT](thumbnails/MYTU/mycobacterium tuberculosis 07.jpg)
![mycobacterium tuberculosis colonies](thumbnails/MYTU/mycobacterium tuberculosis 08.jpg)
![mycobacterium tuberculosis on L-J](thumbnails/MYTU/mycobacterium tuberculosis 09.jpg)
![mycobacterium tuberculosis morphologic characteristics](thumbnails/MYTU/mycobacterium tuberculosis 010.jpg)
![close-up of a Mycobacterium tuberculosis culture](thumbnails/MYTU/mycobacterium tuberculosis 011.jpg)
![mycobacterium tuberculosis culture close-up](thumbnails/MYTU/mycobacterium tuberculosis 012.jpg)
![M.tuberculosis colony close-up](thumbnails/MYTU/mycobacterium tuberculosis 013.jpg)
![mycobacterium tuberculosis close-up](thumbnails/MYTU/mycobacterium tuberculosis 014.jpg)
![M.tuberculosis confluent growth](thumbnails/MYTU/mycobacterium tuberculosis 015.jpg)
![mycobacterium tuberculosis on Löwenstein-Jensen medium](thumbnails/MYTU/mycobacterium-tuberculosis-on-lowenstein-jensen-medium.jpg)
![cultivation media for mycobacterium tuberculosis](thumbnails/MYTU/mycobacterium tuberculosis 03.jpg)
![mycobacterium tuberculosis on Ogawa and Löwenstein-Jensen medium](thumbnails/MYTU/lowenstein-jensen-medium.jpg)
Mycobacterium tuberculosis cultivation
![cultivation of mycobacterium tuberculosis in MB/Bact](thumbnails/MYTU/mb-bact.jpg)
![middlebrook 7H9 broth for MB/Bact](thumbnails/MYTU/middlebrook-7h9-broth.jpg)
Mycobacterium sp.
![mycobacterium fortuitum colonies](thumbnails/MYTU/mycobacterium-fortuitum.jpg)
![mycobacterium fortuitum on Ogawa medium](thumbnails/MYTU/mycobacterium-fortuitum-ogawa.jpg)
![mycobacterium vaccae](thumbnails/MYTU/mycobacterium-vaccae.jpg)
![mycobacterium fortuitum, consistence of mycobacteria colonies](thumbnails/MYTU/mycobacterium-fortuitum-morphology.jpg)
![mycobacterium gordonae](thumbnails/MYTU/mycobacterium-gordonae.jpg)
![mycobacterium kansasii](thumbnails/MYTU/mycobacterium-kansasii.jpg)
Acid-fast stain (Ziehl-Neelsen & Kinyoun's stain)
![acid-fast stained mycobacterial culture specimen](thumbnails/MYTU/mycobacterium tuberculosis 016.jpg)
![cording in mycobacteria](thumbnails/MYTU/mycobacterium tuberculosis 027.jpg)
![m.tuberculosis ziehl-neelsen stain](thumbnails/MYTU/mycobacterium-tuberculosis-ziehl-neelsen-stain.jpg)
![mycobacterium tuberculosis Z-N stain](thumbnails/MYTU/mycobacterium-zn.jpg)
![mycobacterium tuberculosis in sputum, Z-N](thumbnails/MYTU/mycobacterium tuberculosis 019.jpg)
![m.tuberculosis, Koch's bacillus, acid fast rods](thumbnails/MYTU/mycobacterium tuberculosis 026.jpg)
![ziehl-neelsen staining of non-acid-fast bacteria](thumbnails/MYTU/mycobacterium-staphylococcus-ziehl-neelsen.jpg)
![acid-fast and non-acid-fast bacilli, micrograph](thumbnails/MYTU/ziehl-neelsen-stain.jpg)
![Kinyoun's stain](thumbnails/MYTU/kinyoun-stain.jpg)
Mycobacterium tuberculosis SEM & 3D illustrations
![mycobacterium tuberculosis sem](thumbnails/MYTU/mycobacterium tuberculosis 030.jpg)
![mycobacterium tuberculosis, acid-fast rods](thumbnails/MYTU/mycobacterium-tuberculosis-acid-fast-rods.jpg)
![mycobacterium tuberculosis, acid-fast rods](thumbnails/MYTU/mycobacterium-tuberculosis-acid-fast-rods-blue.jpg)
Useful Links
WIKIPEDIACENTERS FOR DISEASE CONTROL AND PREVENTION (CDC)
- Basic TB Facts
- Testing & Diagnosis
- Testing for tuberculosis (TB)
- Treatment of Tuberculosis; American Thoracic Society, CDC, and Infectious Diseases Society of America
- Acid-fast stain
MICROBE LIBRARY