Polyphasic Taxonomic Analysis Establishes Mycobacterium indicus pranii as a Distinct Species

Abstract

Background Mycobacterium indicus pranii (MIP), popularly known as Mw, is a cultivable, non-pathogenic organism, which, based on its growth and metabolic properties, is classified in Runyon Group IV along with M. fortuitum, M. smegmatis and M. vaccae. The novelty of this bacterium was accredited to its immunological ability to undergo antigen driven blast transformation of leukocytes and delayed hypersensitivity skin test in leprosy patients, a disease endemic in the Indian sub-continent. Consequently, MIP has been extensively evaluated for its biochemical and immunological properties leading to its usage as an immunomodulator in leprosy and tuberculosis patients. However, owing to advances in sequencing and culture techniques, the citing of new strains with almost 100% similarity in the sequences of marker genes like 16S rRNA, has compromised the identity of MIP as a novel species. Hence, to define its precise taxonomic position, we have carried out polyphasic taxonomic studies on MIP that integrate its phenotypic, chemotaxonomic and molecular phylogenetic attributes.Methodology/Principal FindingsThe comparative analysis of 16S rRNA sequence of MIP by using BLAST algorithm at NCBI (nr database) revealed a similarity of ≥99% with M. intracellulare, M. arosiense, M. chimaera, M. seoulense, M. avium subsp. hominissuis, M. avium subsp. paratuberculosis and M. bohemicum. Further analysis with other widely used markers like rpoB and hsp65 could resolve the phylogenetic relationship between MIP and other closely related mycobacteria apart from M. intracellulare and M. chimaera, which shares ≥99% similarity with corresponding MIP orthologues. Molecular phylogenetic analysis, based on the concatenation of candidate orthologues of 16S rRNA, hsp65 and rpoB, also substantiated its distinctiveness from all the related organisms used in the analysis excluding M. intracellulare and M. chimaera with which it exhibited a close proximity. This necessitated further analysis of MIP with more sensitive and segregating parameters to ascertain its precise taxonomic position as a new species. The analysis of MIP and its comparison with other mycobacterial reference strains based on cellular and biochemical features, growth characteristics and chemotaxonomic studies like FAME profiling confirmed that MIP is uniquely endowed with diverse metabolic attributes that effectively distinguishes it from all the closely related mycobacteria including M. intracellulare and M. chimaera.ConclusionThe results presented in this study coupled with the non-pathogenic nature and different biochemical and immunomodulatory properties of MIP affirm it as a distinct species belonging to M. avium complex (MAC). It is further proposed to use an earlier suggested name Mycobacterium indicus pranii for this newly established mycobacterial species. This study also exemplifies the growing need for a uniform, consensus based broader polyphasic frame work for the purpose of taxonomy and speciation, particularly in the genus Mycobacterium.

Virulence and Immune Response Induced by Mycobacterium avium Complex Strains in a Model of Progressive Pulmonary Tuberculosis and Subcutaneous Infection in BALB/c Mice

“…The Mycobacterium avium complex (MAC) consists of nine recognized species and a variety of strains that may be members of undescribed taxa (12,28,(38)(39)(40)(41). MAC can induce four distinct clinical syndromes: pulmonary disease, lymphadenitis, disseminated disease, and skin disease (12).…”

Microbiological Features and Clinical Relevance of New Species of the Genus Mycobacterium

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Emerging drugs and alternative possibilities in the treatment of tuberculosis

“…Repeated doses of intradermal heat-killed M. indicus pranii immunotherapy may reduce inflammation associated with TB and increase the CD4 + T-cell count in persons infected with HIV. [52][53][54] Adjunctive therapy with prednisolone for 6 weeks and treatment by M. indicus pranii for 3 months did not have a significant effect on the combined outcome of death from all causes, cardiac tamponade requiring pericardiocentesis, or constrictive pericarditis. [55] Both therapies were also associated with an increased risk of HIV-associated cancer.…”