Mycobacterial Terminology

Laboratory and medical personnel who deal with mycobacteria need a simple, concise descriptor for isolates that are not members of the Mycobacterium tuberculosis complex (MTBC). Although many such isolates will be pathogens, categorical exclusion of MTBC has profound clinical and public health implications. Since the early days of mycobacteriology, writers and speakers have used a variety of terms to describe these mycobacteria, e.g., anonymous, unclassified, opportunist, atypical, environmental, nontuberculosis, nontuberculous, and mycobacteria other than tubercle bacilli (MOTT). None of the terms has universal acceptance, although the majority of authors now use “atypical,” “MOTT,” or “nontuberculous.”

Others have previously expressed the opinion that “nontuberculous” is inappropriate when describing mycobacteria other than MTBC (and the diseases they cause) (1, 2). I share that view. First, to suggest that some mycobacteria literally “do not have tuberculosis” is nonsensical. Second, and more importantly, “nontuberculous” is already used widely in the medical literature to refer to diseases other than tuberculosis, e.g., asbestosis and asthma. There exists, therefore, a potential for misunderstanding. The recent paper by Scarparo et al. (3) in which they report on the evaluation of commercial amplification assays for tuberculosis is a clear illustration of this point. As an example, in the first paragraph of Results, the authors state that “126 specimens were from patients with a diagnosis of tuberculosis, and 170 were from patients with nontuberculous pulmonary disease.” However, in paragraph 4 of Results, the authors state that there were only “151 samples from nontuberculous pulmonary disease” due to the fact that cultures of 19 of 170 specimens “grew nontuberculous mycobacteria.” There would have been less confusion had “nontuberculous” been reserved for the disease and a different term had been used for the mycobacteria.

My personal preference has always been to use “atypical mycobacteria” and “atypical mycobacteriosis” with full acceptance that “atypical” can be criticized on the grounds that species such as Mycobacterium avium and M. kansasii are “typical” mycobacteria. (They are, however, in some ways atypical when compared to the type species of the genus because they are not obligate pathogens.) “Atypical” is short and euphonious and has been widespread in the mycobacterial literature for decades. Finally, it should be noted that a major meeting held in Denver in 1979, sponsored by the National Jewish Hospital with funding from bodies such as the National Institute of Allergy and Infectious Diseases of the National Institute of Health and the American Thoracic Society, was entitled International Conference on Atypical Mycobacteria.