Reclassification of the Mycobacterium tuberculosis Complex (MTBC) Species as Mycobacterium tuberculosis



The species of the Mycobacterium tuberculosis Complex (MTBC)—M. tuberculosis, M. africanum, M. bovis, M. caprae, M. microti, and M. pinnipedii—are very closely related. In this webinar, we will discuss the techniques used to examine the MTBC in order to unravel this taxonomic mystery. Using phylogenomic techniques to compare the type strains of these species, we discovered that all of these “species” are, in fact, M. tuberculosis. We further examined all the strains deposited in GenBank under those species names and found all of them to be strains of M. tuberculosis. All known strains of three other putative MTBC members (“M. canettii”, “M. mungi”, and “M. orygis”) were similarly shown to be strain of M. tuberculosis. We have recently published a paper in the International Journal of Systematic and Evolutionary Microbiology officially unifying the previously separate MTBC species as M. tuberculosis.

Key Points:

  • Using whole-genome sequencing (WGS) and phylogenomic analysis of the MTBC species type strains, we discovered that all of these “species” are, in fact, Mycobacterium tuberculosis
  • By similarly analyzing all the MTBC non-type strain whole-genome sequences (>3,700) in GenBank, we determined that all of these strains similarly should be considered to be strains of Mycobacterium tuberculosis
  • We recommend the use of the infrasubspecific term ‘variant’ and infrasubspecific designations that generally retain the historical nomenclature associated with the groups or otherwise convey such characteristics (e.g., M. tuberculosis variant bovis). 
  • ATCC is currently in the process of updating the nomenclature used in our catalog to reflect this phylogenomically modernized taxonomy.


Marco Riojas

Marco Riojas, Ph.D.,
Scientist, ATCC/BEI Resources

Dr. Riojas has been with ATCC/BEI Resources for over 10 years. He has a Ph.D. in Biodefense, and his primary research interests include biodefense, bacterial systematics, phylogenomics, and genomic identification of species.