[Infection Genetics and Evolution [Volume 8, Issue 1, January 2008, Pages 100-101]

Discussion

The use of the name Mycobacterium w for the leprosy immunotherapeutic bacillus creates confusion with M. tuberculosis-W (Beijing strain): A suggestion

Gursaran Pran Talwar (a), Niyaz Ahmed (b) and Vikram Saini (c)

a Talwar Research Foundation, E-8 Neb Valley, Neb Sarai, New Delhi 110068, India

b Pathogen Evolution Group, Centre for DNA Fingerprinting and Diagnostics (CDFD), Hyderabad, India

c Department of Biochemistry, University of Delhi South Campus, New Delhi, India

Talwar et al., based on a series of investigations, identified an atypical mycobacterium known as Mycobacterium w (Mw), which was subsequently used as a potential leprosy vaccine ([Talwar et al., 1978] and [Talwar, 1999]). Mw was evaluated by phase-wise clinical trials in multibacillary patients as an adjunct to the standard multidrug regime. Immunotherapy with Mw vaccine once every 3 months combined with chemotherapy, significantly accelerated bacillary clearance, expedited clinical recovery and shortened the time for full recovery (Talwar et al., 1990; [Zaheer et al., 1991] and [Zaheer et al., 1993]). It was found to be effective in multibacillary leprosy patients with persistently high bacteriological index despite long-term multidrug therapy (Zaheer et al., 1995). Besides therapeutic benefits, it had immunoprophylactic benefits in household contacts of leprosy patients (Sharma et al., 2005). The Mw vaccine subsequently received approval of the Drugs Controller General of India and is manufactured and marketed by a well-known pharmaceutical company.
Mw shared antigens with both M. leprae and M. tuberculosis despite being distinct from the two. It protected both BCG responder and non-responder genetic strains of mice against M. tuberculosis H37Rv (Singh et al., 1991). There is a strong indication of its immunotherapeutic role in category II tuberculosis (Patel et al., 2002) and large-scale trials are in progress at 10 different centres in India for the treatment of tuberculosis patients. It also revealed benefit as an immunomodulator and adjuvant in bladder cancer (Chaudhuri and Mukhopadhyay, 2003), HIV (Kharkar, 2002) and psoriasis (Rath and Kar, 2003).

Reddi et al. (1994) on the basis of nucleotide sequence in two polymorphic regions, reported Mycobacterium w to be distinct from several other mycobacteria such as M. fortuitum, M. smegmatis, M. chelonane, M. bovis, M. avium, M. intracellulare, M. scrofulaceum, M. kansasii, M. gastri, M. gordonae, M. shimoidei, M. malmoense, M. haemophilum, M. terrae, M. nonchromogenicum, M. triviale, M. marinum, M. flavescens, M. simiae, M. szulgai, M. xenopi, M. asiaticum, M. aurum, M. smegmatis, M. vaccae, M. fortuitum subsp. fortuitum, M. fortuitum subsp. peregrinum, M. chelonane subsp. chelonane, M. chelonane subsp. abscessus and M. genavense. On basis of morphological, colonial, growth and biochemical characteristics, it was classified in Runyon's group IV but was distinguishable from other known species of rapidly growing mycobacteria (Saxena et al., 1978). It was non-pathogenic in mice.

Genetic analysis of Mw points to its belonging to a saprophytic or soil/water dwelling lineage of mycobacteria. Unfortunately, although its novelty has been established by microbiological, biochemical and molecular criteria, this mycobacterium has not been named as an independent species as yet and its taxonomic identity has remained confusing. The name Mw actually originated as a result of the coding given to various known and atypical strains of mycobacteria investigated in the Talwar laboratory. There was no overlap with other mycobacterial names. However, with the advent of molecular fingerprinting and evolutionary genetic approaches, several new strains under different pathogenic and non-pathogenic mycobacterial lineages have been identified and named. Hypervirulent M. tuberculosis-W (Beijing genotype) is one such strain that was termed as ‘W isolate’ (Agerton et al., 1999) to denote a highly drug-resistant group of substrains of Beijing genotype family. Molecular profiling of Mw indeed points to a separate lineage for Mw (Ahmed et al., 2007, unpublished data), the whole genome sequence analyses additionally provides evidence of the existence of substantive and interesting differences with M. tuberculosis as well as other members of the M. tuberculosis complex (V. Saini and colleagues, personal communication). The use of the isolate name ‘Mycobacterium w’ for the leprosy immunotherapeutic bacillus Mw, therefore, gives an impression that Mw is a member of the Beijing family.

Owing to these concerns, we suggest that in order to avoid further confusion and mix-up with the M. tuberculosis-W Beijing strain, the Mycobacterium w (Mw) be referred to as Mycobacterium indicus pranii. The reason for choosing this name is based on the isolation of this bacterium from India (indicus), discovery by Pran Talwar (pranii) and characterization at the National Institute of Immunology (pranii). The 16S ribosomal RNA sequence of this species is deposited in the GenBank (GB accession DQ437715). This and other sequences and cultures of M. indicus pranii are available from authors upon request.

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[Commentary posted here for fair use after permission of the Editor of 'Infection Genetics and Evolution', Professor Seyed E. Hasnain]