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The principal diseases caused by mycobacteria are tuberculosis and leprosy. Descriptions of both diseases can be found in pre-Christian Greek literature and DNA from both has been recovered from ancient skeletons. Leprosy is caused by Mycobacterium leprae and Mycobacterium lepromatosis. Leprosy still exists in many parts of the world but for unknown reasons, it has died out in Europe. Tuberculosis is the best studied mycobacterial disease and is caused by members of the Mycobacterium tuberculosis complex (M. tuberculosis, M. bovis, M. africanum, and M. canetti). Genome analysis has shown that mycobacteria show a large variation in size and that the smallest genomes are found in the pathogenic species (genomic reduction). Genome analysis has not provided an explanation for the inability of Mycobacterium leprae to grow in the laboratory. Genomic analysis has revealed some of the key virulence factors of Mycobacterium tuberculosis and these include the type VII secretion system (known as ESX), the PE and PPE family of proteins, and mycolic acid. The latter helps to protect the bacterium from phagocytosis. Effective protection against tuberculosis is provided by vaccination with either Mycobacterium microti or the BCG strain of Mycobacterium tuberculosis. Both have a deletion of a genomic region encoding three cell wall proteins. Treatment of tuberculosis requires months of antibiotic therapy and multi-drug resistance is common. The use of DNA sequencing can greatly reduce the time to determine antibiotic sensitivity. |
