Abstract

BackgroundMycobacterium intracellulare is a major cause of Mycobacterium avium complex lung disease in many countries. Molecular studies have revealed several new Mycobacteria species that are closely related to M. intracellulare. The aim of this study was to re-identify and characterize clinical isolates from patients previously diagnosed with M. intracellulare lung disease at the molecular level.MethodsMycobacterial isolates from 77 patients, initially diagnosed with M. intracellulare lung disease were re-analyzed by multi-locus sequencing and pattern of insertion sequences.ResultsAmong the 77 isolates, 74 (96 %) isolates were designated as M. intracellulare based on multigene sequence-based analysis. Interestingly, the three remaining strains (4 %) were re-identified as “Mycobacterium indicus pranii” according to distinct molecular phylogenetic positions in rpoB and hsp65 sequence-based typing. In hsp65 sequevar analysis, code 13 was found in the majority of cases and three unreported codes were identified. In 16S–23S rRNA internal transcribed spacer (ITS) sequevar analysis, all isolates of both species were classified within the Min-A ITS sequevar. Interestingly, four of the M. intracellulare isolates harbored IS1311, a M. avium-specific element. Two of three patients infected with “M. indicus pranii” had persistent positive sputum cultures after antibiotic therapy, indicating the clinical relevance of this study.ConclusionsThis analysis highlights the importance of precise identification of clinical isolates genetically close to Mycobacterium species, and suggests that greater attention should be paid to nontuberculous mycobacteria lung disease caused by “M. indicus pranii”.

Highlights

  • Mycobacterium intracellulare is a major cause of Mycobacterium avium complex lung disease in many countries

  • Mycobacterium avium complex (MAC) lung disease is the most common lung disease caused by nontuberculous mycobacteria (NTM) and its prevalence has been increasing worldwide [1,2,3,4,5,6,7,8,9,10]

  • Re-identification of clinical isolates by multigene sequence-based typing Isolates from 77 patients diagnosed with M. intracellulare lung disease were re-identified

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Summary

Introduction

Mycobacterium intracellulare is a major cause of Mycobacterium avium complex lung disease in many countries. Molecular studies have revealed several new Mycobacteria species that are closely related to M. intracellulare. The aim of this study was to re-identify and characterize clinical isolates from patients previously diagnosed with M. intracellulare lung disease at the molecular level. MAC was originally composed of two species, M. avium and Mycobacterium intracellulare [11]. M. intracellulare is a major cause of MAC lung disease in many countries [2]. Molecular studies have revealed the presence of additional taxonomic groups or sequence variants (sequevars) that are closely related to M. intracellulare. Data regarding the proportion of these new species that are etiologic organisms in patients with previously diagnosed M. intracellulare lung disease are very limited

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