Tuberculosis causes
Tuberculosis, or TB is a bacterial infection that kills 3 million people worldwide, more people than any other infection in the world. Approximately one-third of the world is infected, and 15 million people in the US. Active tuberculosis kills 60% of the time if not treated, but treatment cures 90% of patients. Most people are infected with TB have latent TB. This means that the bacteria is controlled by the body's immune system. People with latent TB do not have symptoms and cannot transmit TB to other people. However, later if the infected person has a weakened immune system (AIDS, young children, elderly, sick with other diseases, etc.), the bacteria can break out leading to active TB, or TB disease.
Causes
Bacterial species
The primary cause of TB , Mycobacterium tuberculosis (M. TB), is an aerobic bacterium that divides every 16 to 20 hours, an extremely slow rate compared with other bacteria, which usually divide in less than an hour.[1] (For example, one of the fastest-growing bacteria is a strain of E. coli that can divide roughly every 20 minutes.) Since MTB has a cell wall but lacks a phospholipid outer membrane, it is classified as a Gram-positive bacterium. However, if a Gram stain is performed, MTB either stains very weakly Gram-positive or does not retain dye due to the high lipid & mycolic acid content of its cell wall.[2] MTB is a small rod-like bacillus that can withstand weak disinfectants and survive in a dry state for weeks. In nature, the bacterium can grow only within the cells of a host organism, but M. tuberculosis can be cultured in vitro.[3]
Using certain histological techniques on expectorate samples from phlegm (also called sputum), scientists can identify MTB under a regular microscope. Since MTB retains certain stains after being treated with acidic solution, it is classified as an acid-fast bacillus (AFB).[2] The most common staining technique, the Ziehl-Neelsen stain, dyes AFBs a bright red that stands out clearly against a blue background. Other ways to visualize AFBs include an auramine-rhodamine stain and fluorescent microscopy.
The M. tuberculosis complex includes 3 other TB-causing mycobacteria: M. bovis, M. africanum and M. microti. The first two only very rarely cause disease in immunocompetent people. On the other hand, although M. microti is not usually pathogenic, it is possible that the prevalence of M. microti infections has been underestimated.[4]
Other known pathogenic mycobacteria include Mycobacterium leprae, Mycobacterium avium and M. kansasii. The last two are part of the nontuberculous mycobacteria (NTM) group. Nontuberculous mycobacteria cause neither TB nor leprosy, but they do cause pulmonary diseases resembling TB.[5]
Evolution
During its evolution, M. tuberculosis has lost numerous coding and non-coding regions in its genome, losses that can be used to distinguish between strains of the bacteria. The implication is that M. tuberculosis strains differ geographically, so their genetic differences can be used to track the origins and movement of each strain.[6]
References
- ↑ Cox R (2004). "Quantitative relationships for specific growth rates and macromolecular compositions of Mycobacterium tuberculosis, Streptomyces coelicolor A3(2) and Escherichia coli B/r: an integrative theoretical approach". Microbiology. 150 (Pt 5): 1413–26. PMID 15133103.
- ↑ 2.0 2.1 Madison B (2001). "Application of stains in clinical microbiology". Biotech Histochem. 76 (3): 119–25. PMID 11475314.
- ↑ Parish T, Stoker N (1999). "Mycobacteria: bugs and bugbears (two steps forward and one step back)". Mol Biotechnol. 13 (3): 191–200. PMID 10934532.
- ↑ Niemann S, Richter E, Dalügge-Tamm H, Schlesinger H, Graupner D, Königstein B, Gurath G, Greinert U, Rüsch-Gerdes S (2000). "Two cases of Mycobacterium microti derived tuberculosis in HIV-negative immunocompetent patients". Emerg Infect Dis. 6 (5): 539–42. PMID 10998387.
- ↑ "Diagnosis and treatment of disease caused by nontuberculous mycobacteria. This official statement of the American Thoracic Society was approved by the Board of Directors, March 1997. Medical Section of the American Lung Association". Am J Respir Crit Care Med. 156 (2 Pt 2): S1–25. 1997. PMID 9279284.
- ↑ Rao K, Kauser F, Srinivas S, Zanetti S, Sechi L, Ahmed N, Hasnain S (2005). "Analysis of genomic downsizing on the basis of region-of-difference polymorphism profiling of Mycobacterium tuberculosis patient isolates reveals geographic partitioning". J Clin Microbiol. 43 (12): 5978–82. PMID 16333085.