title: Uncoupling Environmental pH and Intrabacterial Acidification from Pyrazinamide Susceptibility in Mycobacterium tuberculosis.
abstract: Pyrazinamide (PZA) is a first-line antitubercular drug for which the mode of action remains unresolved. Mycobacterium tuberculosis lacks measurable susceptibility to PZA under standard laboratory growth conditions. However, susceptibility to this drug can be induced by cultivation of the bacilli in an acidified growth medium. Previous reports suggested that the active form of PZA, pyrazinoic acid (POA), operates as a proton ionophore that confers cytoplasmic acidification when M. tuberculosis is exposed to an acidic environment. In this study, we demonstrate that overexpression of the PZA-activating enzyme PncA can confer PZA susceptibility to M. tuberculosis under neutral and even alkaline growth conditions. Furthermore, we find that wild-type M. tuberculosis displays increased susceptibility to POA relative to PZA in neutral and alkaline media. Utilizing a strain of M. tuberculosis that expresses a pH-sensitive green fluorescent protein (GFP), we find that unlike the bona fide ionophores monensin and carbonyl cyanide 3-chlorophenylhydrazone, PZA and POA do not induce rapid uncoupling or cytoplasmic acidification under conditions that promote susceptibility. Thus, based on these observations, we conclude that the antitubercular action of POA is independent of environmental pH and intrabacterial acidification.
authors.affiliation: Department of Microbiology and Immunology, Center for Infectious Diseases and Microbiology Translational Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Peterson
authors.affiliation: Department of Microbiology and Immunology, Center for Infectious Diseases and Microbiology Translational Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
authors.forename: Brandon C
authors.initials: BC
authors.lastname: Rosen
authors.affiliation: Department of Microbiology and Immunology, Center for Infectious Diseases and Microbiology Translational Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Dillon
authors.affiliation: Department of Microbiology and Immunology, Center for Infectious Diseases and Microbiology Translational Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA abaughn@umn.edu.
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Baughn
mesh_terms: D000581:Amidohydrolases / Q000235:genetics* / Q000378:metabolism; D000995:Antitubercular Agents / Q000378:metabolism / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000187:drug effects* / Q000235:genetics; D015870:Gene Expression; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006835:Hydrazones / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests; D008985:Monensin / Q000494:pharmacology; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D061209:Proton Ionophores / Q000494:pharmacology; D011522:Protons; D011718:Pyrazinamide / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D000995:Antitubercular Agents; D006835:Hydrazones; D061209:Proton Ionophores; D011522:Protons; C070053:carbonyl 3-chlorophenylhydrazone; D049452:Green Fluorescent Proteins; D011718:Pyrazinamide; C005296:pyrazinoic acid; D008985:Monensin; D000581:Amidohydrolases; C487496:PncA protein, Mycobacterium tuberculosis