Iron enhances the susceptibility of pathogenic mycobacteria to isoniazid, an antitubercular drug

  • Manjula Sritharan
  • Veena C. Yeruva
  • Sivagamisundaram C. Sivasailappan
  • Sridevi Duggirala


The catalase-peroxidase KatG of Mycobacterium tuberculosis plays a central role in the mechanism of action of the anti-tubercular drug isoniazid (INH). Like other bacterial catalases, mycobacterial catalase-peroxidases are dual active enzymes with both catalase and peroxidase activities in the same protein molecule. In our previous study, we showed that iron deprivation resulted in the loss of peroxidase activity in several non-pathogenic mycobacterial species. Here we extended the study to pathogenic mycobacteria and showed that the peroxidase activity, associated with iron-sufficient (4 µg Fe/ml) conditions of growth was responsible for INH activation. Upon iron deprivation (0.02 µg Fe/ml), peroxidase activity was abolished and there was no activation of INH, as demonstrated both by INH-mediated NBT reduction (spectrophotometrically and activity staining in gels) and by viability studies as assayed by the microplate Alamar Blue assay (MABA). In the viability assay, iron-sufficient M. tuberculosis, Mycobacterium bovis and Mycobacterium bovis BCG were susceptible to INH and iron-deficient organisms expressing negligible peroxidase survived high concentrations of the drug. It␣is well known that M. tuberculosis is sensitive to low concentrations of INH while the minimum inhibitory concentration of the drug is quite high for other mycobacteria, especially the non-pathogenic species. We showed this difference to be due to the specificity of the peroxidase for the drug. As withholding of iron is one of the host’s mechanisms of controlling an invading pathogen, the implications of these observations on the efficacy of the anti-tubercular drug INH are discussed with reference to the iron status within the human host.


Catalase-peroxidases Mycobacteria Iron Isoniazid Alamar Blue assay 



The financial assistance for establishment of the containment facility at P3 level by the Andhra Pradesh–Netherlands Biotechnology Programme is gratefully acknowledged. CAS Sivagami Sundaram, JRF under the UPE programme and Ms. Veena in the ILS project acknowledge the University of Hyderabad for financial support. Sridevi Duggirala is supported by fellowship from University Grants Commission (UGC), India.


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Copyright information

© Springer Science+Business Media B.V. 2006 2006

Authors and Affiliations

  • Manjula Sritharan
    • 1
  • Veena C. Yeruva
    • 1
  • Sivagamisundaram C. Sivasailappan
    • 1
  • Sridevi Duggirala
    • 1
  1. 1.Department of Animal SciencesUniversity of HyderabadHyderabadIndia

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