“Mycobacterium indicus pranii” Is a Strain of Mycobacterium intracellulare

In the recent publication “Comparative Analyses of Nonpathogenic, Opportunistic, and Totally Pathogenic Mycobacteria Reveal Genomic and Biochemical Variabilities and Highlight the Survival Attributes of Mycobacterium tuberculosis,” Rahman et al. (1) used bioinformatic methods to examine the evolutionary relatedness and metabolic capacity of mycobacteria of diverse pathogenic potential. A key conclusion of this work is the suggestion that “M. indicus pranii . . . is a predecessor of the M. avium complex and is at an evolutionarily transitory position with respect to a fast versus slow grower and as a saprophyte versus a seasoned pathogen.” In contrast, we suggest that this work provides strong evidence that “Mycobacterium indicus pranii” is a strain of Mycobacterium intracellulare. The mycobacterial isolate currently known as “M. indicus pranii” was first described in the 1970s as “Mycobacterium w” and, due to some unusual immunomodulatory and biochemical properties, it has been proposed that this organism represents a distinct species (2). However, neither of its names is found on the List of Prokaryotic Names with Standing in Nomenclature, and the designation “Mycobacterium indicus pranii” does not conform to the binomial naming convention used for bacterial species (3). Despite assertions that “M. indicus pranii” has a distinctive phenotypic profile, we are unaware of any studies that directly compare this organism with a comprehensive panel of M. intracellulare or Mycobacterium avium complex strains. In any case, many Mycobacterium spp. exhibit intraspecies diversity. M. avium encompasses environmental isolates and professional pathogens with diverse nutritional requirements and growth characteristics (4). Mycobacterium bovis is a facultative mammalian pathogen, whereas strains of M. bovis Bacille Calmette-Guérin (BCG) are used as vaccines against tuberculosis and immunotherapeutic agents for treatment of bladder cancer (5). Because phenotypic results can be misleading, sequencingbased approaches are crucial to the accurate identification and