Acid-fast, obligate aerobic, non-motile, rod-shaped bacterium, this is the causative agent of tuberculosis. Tuberculosis is, to this day, according to the WHO, the leading killer of adults, with approximately 2 million deaths annually worldwide. It is estimated that 8 million people are infected each year. A large part of its success as a pathogen is due to its ability to persist in a dormant or latent form for years or even decades, with a concomitant absence of clinical symptoms. This non-replicating persistent form is refractory to most drugs, it may be induced by hypoxia (oxygen depletion) and/or nitric oxide exposure. Up to one-third of the world's population is thought to be latently infected. An additional problem is the emergence of drug resistant strains, mainly because people do not complete their treatment plans or have been incorrectly treated and so have remained infectious. Mycobacteria have an unusual outer membrane approximately 8 nm thick, despite being considered Gram-positive. The outer membrane and the mycolic acid-arabinoglactan-peptidoglycan polymer form the cell wall, which constitutes an efficient permeability barrier in conjunction with the cell inner membrane.

Strain Erdman was isolated from human sputum by W.H. Feldman in 1945, at the Mayo Clinic, Rochester, MN, and deposited with the Trudeau Mycobacterium Culture Collection in 1946. Due to its consistently high virulence, it has been widely used as a standard virulent laboratory strain for virulence and immunization studies. It has a faster in vivo doubling time than two attenuated strains, M. tuberculosis H37Ra and Mycobacterium bovis Bacillus Calmette-Guerin (BCG), and a slightly faster in vivo doubling time than the virulent H37Rv strain in mice (adapted from PMID 22535945).