title: Molecular genetics of para-aminosalicylic acid resistance in clinical isolates and spontaneous mutants of Mycobacterium tuberculosis.
abstract: The emergence of Mycobacterium tuberculosis resistant to first-line antibiotics has renewed interest in second-line antitubercular agents. Here, we aimed to extend our understanding of the mechanisms underlying para-aminosalicylic acid (PAS) resistance by analysis of six genes of the folate metabolic pathway and biosynthesis of thymine nucleotides (thyA, dfrA, folC, folP1, folP2, and thyX) and three N-acetyltransferase genes [nhoA, aac(1), and aac(2)] among PAS-resistant clinical isolates and spontaneous mutants. Mutations in thyA were identified in only 37% of the clinical isolates and spontaneous mutants. Overall, 24 distinct mutations were identified in the thyA gene and 3 in the dfrA coding region. Based on structural bioinformatics techniques, the altered ThyA proteins were predicted to generate an unfolded or dysfunctional polypeptide. The MIC was determined by Bactec/Alert and dilution assay. Sixty-three percent of the PAS-resistant isolates had no mutations in the nine genes considered in this study, revealing that PAS resistance in M. tuberculosis involves mechanisms or targets other than those pertaining to the biosynthesis of thymine nucleotides. The alternative mechanism(s) or pathway(s) associated with PAS resistance appears to be PAS concentration dependent, in marked contrast to thyA-mutated PAS-resistant isolates.
authors.affiliation: Laboratory of Molecular Pathology of Tuberculosis, Pasteur Institute, Scientific Institute of Public Health, Brussels, Belgium.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Mathys
authors.forename: René
authors.initials: R
authors.lastname: Wintjens
authors.forename: Philippe
authors.initials: P
authors.lastname: Lefevre
authors.forename: Julie
authors.initials: J
authors.lastname: Bertout
authors.forename: Amit
authors.initials: A
authors.lastname: Singhal
authors.forename: Mehdi
authors.initials: M
authors.lastname: Kiass
authors.forename: Natalia
authors.initials: N
authors.lastname: Kurepina
authors.forename: Xiao-Ming
authors.initials: XM
authors.lastname: Wang
authors.forename: Barun
authors.initials: B
authors.lastname: Mathema
authors.forename: Alain
authors.initials: A
authors.lastname: Baulard
authors.forename: Barry N
authors.initials: BN
authors.lastname: Kreiswirth
authors.forename: Pablo
authors.initials: P
authors.lastname: Bifani
mesh_terms: D010131:Aminosalicylic Acid / Q000494:pharmacology*; D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D005492:Folic Acid / Q000096:biosynthesis; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D013329:Structure-Activity Relationship; D013940:Thymidylate Synthase / Q000235:genetics*; D013941:Thymine / Q000096:biosynthesis
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D010131:Aminosalicylic Acid; D005492:Folic Acid; D013940:Thymidylate Synthase; D013941:Thymine