Mechanisms of Pyrazinamide Action and Resistance.

Pyrazinamide (PZA) is a unique antituberculosis (anti-TB) drug that plays a key role in shortening TB therapy. PZA kills nonreplicating persisters that other TB drugs fail to kill, which makes it an essential drug for inclusion in any drug combinations for treating drug-susceptible and drug-resistant TB such as multidrug-resistant TB. PZA acts differently from common antibiotics by inhibiting multiple targets such as energy production, trans-translation, and perhaps pantothenate/coenzyme A required for persister survival. Resistance to PZA is mostly caused by mutations in the pncA gene encoding pyrazinamidase, which is involved in conversion of the prodrug PZA to the active form pyrazinoic acid. Mutations in the drug target ribosomal protein S1 (RpsA) are also found in some PZA-resistant strains. The recent finding that panD mutations are found in some PZA-resistant strains without pncA or rpsA mutations may suggest a third PZA resistance gene and a potential new target of PZA. Current phenotype-based PZA susceptibility testing is not reliable due to false resistance; sequencing of the pncA gene represents a more rapid, cost-effective, and reliable molecular test for PZA susceptibility testing and should be used for guiding improved treatment of multidrug-resistant and extensively multidrug-resistant TB. Finally, the story of PZA has important implications for not only TB therapy but also chemotherapy in general. PZA serves as a model prototype persister drug and hopefully a "tipping point" that inspires new efforts at developing a new type of antibiotic or drug that targets nonreplicating persisters for improved treatment of not only TB but also other persistent bacterial infections.