title: Molecular analysis of isoniazid-resistant Mycobacterium tuberculosis isolates from England and Wales reveals the phylogenetic significance of the ahpC -46A polymorphism.
abstract: The present study investigated the prevalence and diagnostic potential of the most commonly reported mutations associated with isoniazid resistance, katG 315Thr, katG 315Asn, inhA -15T, inhA -8A, and the oxyR-ahpC intergenic region, in a population sample of 202 isoniazid-resistant Mycobacterium tuberculosis isolates and 176 randomly selected fully sensitive isolates from England and Wales identified by using a directed oligonucleotide array and limited DNA sequencing. The strains were recovered from patients originating from 29 countries; 41 isolates were multidrug resistant. Mutations affecting katG 315, the inhA promoter, and the oxyR-ahpC intergenic region were found in 62.7, 21.9, and 30% of 169 genotypically distinct isoniazid-resistant isolates, respectively, whereas they were found in 0, 0, and 8% of susceptible strains, respectively. The frequency of mutation at each locus was unrelated to the resistance profile or previous antituberculous drug therapy. The commonest mutation in the oxyR-ahpC intergenic region, ahpC -46A, was present in 23.7% of isoniazid-resistant isolates and 7.5% of susceptible isolates. This proved to be a phylogenetic marker for a subgroup of M. tuberculosis strains originating on the Indian subcontinent, which shared IS6110-based restriction fragment length polymorphism and spoligotype features with the Delhi strain and Central Asian strain CAS1; and this marker is strongly associated with isoniazid resistance and the katG 315Thr mutation. In total, 82.8% of unrelated isoniazid-resistant isolates could be identified by analysis of just two loci: katG 315 and the inhA promoter. Analysis of the oxyR-ahpC intergenic region, although phylogenetically interesting, does not contribute significantly to further identification of isoniazid-resistant isolates.
authors.affiliation: HPA Mycobacterium Reference Unit, Department of Microbiology, Guy's, King's and St Thomas' School of Medicine, King's College Hospital, East Dulwich Grove, London SE22 8QF, United Kingdom.
authors.forename: L V
authors.initials: LV
authors.lastname: Baker
authors.forename: T J
authors.initials: TJ
authors.lastname: Brown
authors.forename: O
authors.initials: O
authors.lastname: Maxwell
authors.forename: A L
authors.initials: AL
authors.lastname: Gibson
authors.forename: Z
authors.initials: Z
authors.lastname: Fang
authors.forename: M D
authors.initials: MD
authors.lastname: Yates
authors.forename: F A
authors.initials: FA
authors.lastname: Drobniewski
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004739:England; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology*; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D009693:Nucleic Acid Hybridization; D020411:Oligonucleotide Array Sequence Analysis; D010544:Peroxidases / Q000235:genetics*; D054464:Peroxiredoxins; D010802:Phylogeny; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D014852:Wales
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D010544:Peroxidases; D054464:Peroxiredoxins; D007538:Isoniazid