title: An upstream truncation of the furA-katG operon confers high-level isoniazid resistance in a Mycobacterium tuberculosis clinical isolate with no known resistance-associated mutations.
abstract: Although the major causes of isoniazid (INH) resistance in Mycobacterium tuberculosis are confined to structural mutations in katG and promoter mutations in the mabA-inhA operon, a significant proportion of INH-resistant strains have unknown resistance mechanisms. Recently, we identified a high-level INH-resistant M. tuberculosis clinical isolate, GB005, with no known resistance-associated mutations. A comprehensive study was performed to investigate the molecular basis of drug resistance in this strain. Although no mutations were found throughout the katG and furA-katG intergenic region, the katG expression and the catalase activity were greatly diminished compared to those in H37Rv (P < 0.01). Northern blotting revealed that the katG transcript from the isolate was smaller than that of H37Rv. Sequencing analysis of furA and upstream genes discovered a 7.2-kb truncation extended from the 96th base preceding the initiation codon of katG. Complementation of the M. tuberculosis Δ(furA-katG) strain with katG and different portions of the truncated region identified a 134-bp upstream fragment of furA that was essential for full catalase activity and INH susceptibility in M. tuberculosis. The promoter activity of this fragment was also shown to be stronger than that of the furA-katG intergenic region (P < 0.01). Collectively, these findings demonstrate that deletion of the 134-bp furA upstream fragment is responsible for the reduction in katG expression, resulting in INH resistance in GB005. To our knowledge, this is the first report showing that deletion of the upstream region preceding the furA-katG operon causes high-level INH resistance in a clinical isolate of M. tuberculosis.
authors.affiliation: Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hong Kong, Special Administrative Region, China gilman.siu@polyu.edu.hk.
authors.forename: Gilman Kit Hang
authors.initials: GK
authors.lastname: Siu
authors.affiliation: Department of Microbiology, Queen Mary Hospital, The University of Hong Kong, Hong Kong, Special Administrative Region, China Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, Special Administrative Region, China.
authors.forename: Wing Cheong
authors.initials: WC
authors.lastname: Yam
authors.affiliation: Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Microbiology, Queen Mary Hospital, The University of Hong Kong, Hong Kong, Special Administrative Region, China Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, Special Administrative Region, China.
authors.forename: Richard Y T
authors.initials: RY
authors.lastname: Kao
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D007538:Isoniazid / Q000494:pharmacology*; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D009876:Operon / Q000235:genetics*; D018088:Tuberculosis, Multidrug-Resistant / Q000235:genetics
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D002374:Catalase; D007538:Isoniazid
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