Objective: To investigate the mechanism of the action and the target of pyrazinamide (PZA), by examining the effect of nutrient-starved conditions on PZA activity.
Methods: M. tuberculosis starved in PBS for 3, 5 or 10 days were treated with PZA, and with benzoic acid, salicylic acid or fatty acid in combination with PZA. The activity of PZA against M.tuberculosis was determined by the number of colony-forming unit (CFU). The membrane potential of M.tuberculosis was determined by flow-cytometry with Rhodamine to investigate the mechanism of PZA activity.
Results: The CFU of M. tuberculosis treated with PZA for 0, 3, 5, 10 days nutrient starvation compared with their respective controls, decreased by 23.08%, 37.75%, 82.32%, 81.03%, respectively. The membrane potential of M. tuberculosis in nutrient-starved cultures declined rapidly over the first 5 days' starvation. The starved bacilli treated with PZA had significantly lower level of membrane potential compared with the control. The effect of PZA on lowering the membrane potential was antagonized by addition of glucose, which provided energy for the bacilli. Fatty acids, benzoic acid and salicylic acid-enhanced PZA activity in both normal and starved bacilli, especially in starved bacilli.
Conclusion: Nutrient starved incubation conditions and weak acids could enhance pyrazinamide activity against Mycobacterium tuberculosis. PZA can impair Mycobacterium tuberculosis cell viability by disrupting the energy supply system and reducing membrane potential of the cells.