title: New mutations in pncA of in vitro selected pyrazinamide-resistant strains of Mycobacterium tuberculosis.
abstract: Mutations within the pncA gene can cause pyrazinamide (PZA) resistance in Mycobacterium tuberculosis. To study further the mutational events leading to PZA resistance, a H37Rv PZA-susceptible strain was used to derive PZA-resistant mutants in vitro. This parental strain was grown at gradually increased concentrations of PZA (from 200 up to 500 microg/ml). A total of eight variant strains were selected for further study. PZA resistance was selected at 250 microg/ml or higher. Seven of them lost PZase activity and hence were PZA resistant. The remaining strain has shown a functional PZase and hence was sensitive to PZA after being exposed to 200 microg/ml PZA. Sequence analysis shows different novel mutations within the pncA gene of these variants. Two silent mutations at nucleotide 6 (G --> A) and 300 (C --> T) were found in the PZA-sensitive variant. Among the seven PZA-resistant variants, there were three deletion mutations found at nucleotide 78 (G), 79 (A), and 143 (A), all resulting in a frameshift, and one nonsense mutation at nucleotide 102 (C --> G), creating a stop codon TAG. It was observed that the mutations found in the pncA gene of these PZA-resistant mutants show a distinctive pattern: mutation positions moved toward the beginning of the open reading frame correlating with the increase in PZA concentration, suggesting a possible relationship between the increase of PZA concentration and the early occurrence of mutations on the pncA gene.
authors.affiliation: Department of Infectious Diseases and Medical Microbiology, Division of Investigative Science, Imperial College School of Medicine, London, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Bamaga
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: D J
authors.initials: DJ
authors.lastname: Wright
mesh_terms: D000581:Amidohydrolases / Q000235:genetics* / Q000378:metabolism; D000995:Antitubercular Agents / Q000494:pharmacology*; D017931:DNA Primers; D004269:DNA, Bacterial / Q000235:genetics; D004352:Drug Resistance, Microbial; D016678:Genome; D007538:Isoniazid / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics*; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics*; D011718:Pyrazinamide / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D000995:Antitubercular Agents; D017931:DNA Primers; D004269:DNA, Bacterial; D011718:Pyrazinamide; D000581:Amidohydrolases; C022490:pyrazinamide deamidase; D007538:Isoniazid