Query: NC_016768:2764000 Mycobacterium tuberculosis KZN 4207 chromosome, complete genome Lineage: Mycobacterium tuberculosis; Mycobacterium; Mycobacteriaceae; Actinomycetales; Actinobacteria; Bacteria General Information: Like other closely related Actinomycetales, such as Nocardia and Corynebacterium, mycobacteria have unusually high genomic DNA GC content and are capable of producing mycolic acids as major components of their cell wall. This bacterium is the causative agent of tuberculosis - a chronic infectious disease with a growing incidence worldwide. It infects 1.7 billion people a year (~33% of the entire world population) and causes over 3 million deaths/year. This bacterium does not form a polysaccharide capsule, and is an extremely slow growing obligate aerobe. This bacterium does not form a polysaccharide capsule, and is an extremely slow growing obligate aerobe. This bacterium does not form a polysaccharide capsule, and is an extremely slow growing obligate aerobe. The sluggish growth rate is a result of the tough cell wall that resists the passage of nutrients into the cell and inhibits waste products to be excreted out of the cell. The specialized cell envelope of this organism resembles a modified Gram positive cell wall. It also contains complex fatty acids, such as mycolic acids, that cause the waxy appearance and impermeability of the envelope. These acids are found bound to the cell envelope, but also form cord factors when linked with a carbohydrate component to form a cord-like structure. Primary infection occurs by inhalation of the organism in droplets that are aerosolized by an infected person. The organism initially replicates in cells of the terminal airways, after which it is taken up by, and replicates in, alveolar macrophages. Macrophages distribute the organism to other areas of the lungs and the regional lymph nodes. Once a cell-mediated hypersensitivity immune response develops, replication of the organism decreases and the bacteria become restricted to developing granulomas.
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General Information: The Republic of Djibouti, Africa appears to be an exceptional place in terms of tuberculosis (TB) caused by Mycobacterium canettii, a highly unusual tubercle bacillus with unusual smooth colony morphology (STB) related to the M. tuberculosis complex (MTBC). M. canettii was first isolated from a 20-year-old French farmer suffering from pulmonary tuberculosis by G. Canetti in 1969. Since then, this strain has been isolated on rare occasions from patients who lived or were presumably infected in East Africa. It tends to preferentially affect children and foreigners in the Horn of Africa. M. canettii, a possible ancestor of the MTBC, is found almost exclusively in the Horn of Africa where TB is thought to have emerged about 40 000 years ago, coinciding with the expansion of human population out of Africa. The geographical restriction of M. canettii isolates and contrasting genetic diversity are characteristics compatible with a non-human reservoir. With the larger pan-genome reflecting the ancestral, wider gene pool of tubercle bacilli, their lower virulence and faster growth, especially at temperatures below 37 degrees C, plausibly reflecting broader environmental adaptability, STB strains might thus come nearer to the as-yet-unknown missing link between the obligate pathogen M. tuberculosis and environmental mycobacteria (adapted from PMIDs 20831613 and 23291586). Mycobacteria have an unusual outer membrane approximately 8nm thick, despite being considered Gram-positive. The outer membrane and the mycolic acid-arabinoglactan-peptidoglycan polymer form the cell wall, which constitutes an efficient permeability barrier in conjunction with the cell inner membrane.