NC_012943:476500 Mycobacterium tuberculosis KZN 1435 chromosome, complete genome
Host Lineage: Mycobacterium tuberculosis; Mycobacterium; Mycobacteriaceae; Actinomycetales; Actinobacteria; Bacteria
General Information: M. tuberculosis strain KZN 1435 was isolated from a patient in KwaZulu-Natal, South Africa. This strain is multidrug-resistant (resistant to isoniazid and rifampin). This bacterium is the causative agent of tuberculosis - a chronic infectious disease with a growing incidence worldwide. This species is responsible for more morbidity in humans than any other bacterial disease. 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. 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. The envelope contains the typical polypeptide layer, the peptidoglycan layer, and free lipids. 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. These fatty acid-carbohydrate complexes inhibit phago-lysosome fusion and are often considered to be indicators of virulent strains. The cell envelope also includes adhesins and aggressions, but does not contain any known toxins. 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.