New Evolutionary Scenario and Molecular Diagnostic Methods in typing of Mycobacterium Tuberculosis Complex strains

Abstract

Tuberculosis is one of the major health problems responsible for morbidity and mortality particularly in developing countries. It is a bacterial disease caused by a group of closely related species of Mycobacterium tuberculosis complex such as M. tuberculosis, Mycobacterium Canetti, Mycobacterium Africanum, Mycobacterium microti, M. bovis, Mycobacterium caprae and Mycobacterium pinnipedii have genetic similarity. The Mycobacterium Tuberculosis Complex (MTBC) species are closely related taxonomic group of bacteria contributing to hundred-percent chromosomal homology between each other. The genome of MTBC is about 4.4 M bp and contains 0.01-0.3 percent synonymic nucleotide polymorphisms. It is characterized by 99.9% similarity at the nucleotide level and identical 16S rRNA sequences but differs widely in host related tropisms, phenotypes, and pathogenicity. MBTC strains have emerged from a common origin through DNA deletion and insertion mechanisms which resulted in the present Mycobacterium species. These insertion –deletion in the variable region of genomes or region of difference (RD) of the MBTC is used to identify the phylogenetic relationships between strains of the M. tuberculosis complex and M. tuberculosis. The deletion of genomic or DNA region reflected RD or evolutionary lineages of M. africanum, M. microti and M. bovis that diverged from the progenitor of the present M. tuberculosis strains. The presence of conservation in the house keeping genes of the species of M. tuberculosis complex causes a rapid evolutionary and emerging processes. There are advanced genotyping tools that are widely used to differentiate Mycobacterium tuberculosis strains. The widely used diagnostic methods are; IS6110 restriction fragment length polymorphism, Spoligotyping, and mycobacterial interspersed repeat units variable number of tandem repeats. These techniques would help for understanding molecular mechanisms and identification of mycobacterial strains to institute the nature of their diversity on the phylogenetic tree that could aid to know the evolutionary situation of emerging strains. Therefore, the need to adopt advanced molecular tools to decipher circulating strains of MTBC should be encouraged.