Also known as: Tuberculosis, TB
Industry of interest: Healthcare
Microbiology: Mycobacterium tuberculosis is an aerobic, acid-fast microorganism that has a highly unusual cell surface that is made up of various lipids and mycolic acid. It does not produce a Gram stain response due to its waxy cell membrane but is generally classified as Gram-positive due to its lack of an outer cell membrane.
Habitat and transmission: M. tuberculosis is spread into the environment in droplet nuclei produced when an infected individual coughs or sneezes (Russell et al., 2010). The droplets are small enough to remain airborne for several hours until inhaled by an unsuspecting individual.
Treatment and antibiotic resistance: Currently treatment for TB requires administration of anti-TB drugs such as isoniazid for 6-12 months (Russell et al., 2010). The drugs in common usage preferentially target replicating organisms. Therefore any dormant organisms in the granuloma will not be affected and may acquire drug resistance (Russell et al., 2010). This in itself may be part of the reason for long treatment regimens. In fact multidrug-resistant strains of M. tuberculosis are on the increase and complicate the treatment of an already problematic microorganism.
Prevention and control: Bacillus Calmette Guérin (BCG) is the only approved anti-TB vaccine. It is used to protect children against the effects of more severe forms of disease such as TB meningitis or disseminated infection (Russell et al., 2010). However the BCG vaccine has limitations in that it does not protect against all manifestations of TB and has been shown to be ineffective in some populations, e.g. India (Russell et al., 2010). Drug development should focus on reducing the duration of treatment time as patient compliance is poor over such a protracted period (Russell et al., 2010). M. tuberculosis is a very hardy microorganism as a result of its waxy cell membrane and is resistant to many commonly used disinfectants. A combination of drugs, vaccines, infection control procedures, good personal hygiene and public health surveillance and screening should minimise transmission of TB.
Disease and symptoms: Upon inhalation of the microorganism the cell is phagocytosed by alveolar macrophages. M. tuberculosis can prevent formation of the phagolysosome in phagocytes. The microorganism can then invade the epithelial cells of the lung causing localised inflammation and recruitment of phagocytic cells (Kirschner et al., 2010). The build up of these cells then results in the formation of granulomas, which are arranged in a roughly spherical structure (Kirschner et al., 2010). The granuloma serves as a microenvironment where cells interact and balance pro- and anti-inflammatory cytokines driving pathology (Kirschner et al., 2010). Symptoms of TB infection include a productive cough, loss of appetite, fever, weight loss and night sweats. TB infection can also be latent (latent TB), lying dormant with no apparent symptoms. A person is not infective in the latency period. Latent infection can become active if the person becomes immunocompromised.
Kirschner D.E., Young D. And Flynn J.L. (2010) Tuberculosis: global approaches to a global disease. Curr Opin Biotechnol. 21(4): 524-531.
Russell D.G., Barry C.E. and Flynn J.L. (2010) Tuberculosis: what we don’t know can, and does, hurt us. Science. 328(5890): 852-856.