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Lung India Official publication of Indian Chest Society  
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Year : 2017  |  Volume : 34  |  Issue : 6  |  Page : 499-505

Effect of efflux pump inhibitors on the susceptibility of Mycobacterium tuberculosis to isoniazid

1 Department of Pulmonary Medicine, King Georg's Medical University, Lucknow, Uttar Pradesh, India
2 Department of Microbiology, King Georg's Medical University, Lucknow, Uttar Pradesh, India

Correspondence Address:
Amita Jain
Department of Microbiology, King Georg's Medical University, Lucknow - 226 003, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-2113.217567

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Background: Mycobacterium can develop drug resistance (DR) by mutation of its existing gene. However, the existence of DR without mutation shows the need to look for an alternative mechanism such as the role of efflux pumps. In this study, we examined the effect of efflux pump inhibitors on isoniazid (INH) susceptibility in clinical isolates of Mycobacterium tuberculosis (Mtb). Materials and Methods: Resazurin microtiter assay was used to examine the effect of efflux pump inhibitors on minimum inhibitory concentration (MIC) levels of INH in eighteen Mtb clinical isolates. Results: The observed reduction in INH-MIC was 2–16-fold in INH-resistant isolates with katG and inhA gene mutations, 2–8-fold in INH-resistant isolates without mutation and 2–4-fold in INH-sensitive isolates. The MIC reduction by verapamil (VER) was observed in 83% isolates, by carbonyl cyanide m-chlorophenylhydrazone (CCCP) 61% isolates, by chloropromazine (CPZ) 61% isolates, by reserpine (RES) in 61% isolates and by 2,4-dinitro phenol (DNP) in 55% isolates. Interpretation and Conclusions: The results obtained in this study confirm that MIC of INH decreased in the presence of efflux pump inhibitors (VER, CCCP, CPZ, DNP, RES) in clinical isolates of Mtb and that the inhibition of efflux pumps by the efflux pump inhibitors can enhance the clinical effect of a drug. The results showed that these efflux pump inhibitors are active against both drug susceptible and drug resistant isolates, indicating that the effect of efflux pump inhibitors is not dependent on the mutational profile of the isolate. We observed in this study that VER was the most effective efflux pump inhibitor.

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