Synergistic Response of Rifampicin with Hydroperoxides on Mycobacterium: A Mechanistic Study

Abstract

Prolonged chemotherapy as well as rapid development of antimicrobial resistance are two of the major concerns for treatment of mycobacterial infections. To enhance the effectiveness of current drug regimens, search for compounds having synergistic interaction with anti-mycobacterial drugs has become indispensable. Here, we have investigated the intervention by oxidative stress, a major factor in mycobacterial pathogenesis, in combination with rifampicin (RIF), a first-line drug used against Mycobacterium tuberculosis. We have observed that a sub-inhibitory concentration of cumene hydroperoxide (CHP), a hydrophobic oxidant, synergistically reduced the minimum inhibitory concentration of RIF by fourfold, with a Fractional Inhibitory Concentration Index (FICI) of 0.45. Also, this interaction was found to be robust and synergistic against different strains of M. smegmatis as well as on M. bovis BCG, with FICI ranging from 0.3 to 0.6. Various physiological, biochemical and molecular parameters were explored to understand the mechanism of synergy. It was observed that increased membrane permeability owing to the presence of the oxidant, led to higher uptake of the drug. Moreover, downregulation of the hydroperoxide reductases by RIF, a transcriptional inhibitor, prevented quenching of the reactive oxygen species produced in the presence of CHP. The lipid soluble reactive species triggered autocatalytic lipid peroxidation (LPO), observed here as extensive membrane damage eventually leading to growth inhibition. Furthermore, it was seen that in combination with hydrogen peroxide (H2O2), the effect was only additive, establishing LPO as a key aspect leading toward synergism. To conclude, this work suggests that targeting the bacterial membrane by a radical species can have a significant impact on the treatment of tuberculosis.

ZnO Nanoparticles and Rifampicin Synergistically Damage the Membrane of Mycobacteria

“…Furthermore, to check the importance of ROS in bacteria, cells were treated with an antioxidant, ascorbic acid . If ROS was involved in the inhibitory action of ZnO NPs and RIF, the inhibitory effect should be lost upon the addition of ascorbic acid . The MIC of ascorbic acid was found to be 6400 μg/mL.…”

“…A 50:50 mixture of acetonitrile and acidified water at pH 2.27 with orthophosphoric acid was used as a mobile phase. The flow rate used was 1.2 mL/min, and eluted RIF was measured with a UV detector at 333 nm …”

“…The flow rate used was 1.2 mL/min, and eluted RIF was measured with a UV detector at 333 nm. 38 3. RESULTS AND DISCUSSION 3.1.…”

The evaluation of the anti‐cancer drug elesclomol that forms a redox‐active copper chelate as a potential anti‐tubercular drug

“…The conversion of resazurin (blue/purple) to resorufin (red/pink) is a direct indication of mycobacterial viability. The minimum concentration at which no growth was observed visually was taken as the MIC . The FICI for each compound was calculated as follows . …”

Inhibitory activity of traditional plants against Mycobacterium smegmatis and their action on Filamenting temperature sensitive mutant Z (FtsZ)—A cell division protein

“…MIC of RIF reduced from 0.015 to 0.00048 mg/mL when given in combination with antitubercular drug SQ109 against M. tuberculosis strain H37R V [60]. Cumene hydroperoxide reduced the MIC of RIF by 16-fold against M. tuberculosis strain H37R V [61].…”