title: Characteristics of embB mutations in multidrug-resistant Mycobacterium tuberculosis isolates in Henan, China.
abstract: OBJECTIVE
  To determine the association between embB mutations and drug resistance, and to further investigate the mechanism of embB mutations involved in the development of ethambutol and multidrug resistance in Mycobacterium tuberculosis.
  
  
  METHODS
  One hundred and thirty-eight multidrug-resistant clinical M. tuberculosis isolates, including 86 ethambutol-resistant and 52 ethambutol-susceptible strains, were analysed to characterize mutations within the entire coding region of the embB gene. Moreover, a two-step genotyping was performed to identify the genetic lineage.
  
  
  RESULTS
  In total, 27 embB mutation types were detected in 19 distinct codons. Though a strong association was observed between embB mutations and ethambutol resistance, 19.2% of embB306 mutants and 11.5% of embB406 or embB497 mutants were ethambutol susceptible. Among 39 ethambutol-resistant strains without embB306 mutations, 51.3% harboured mutations at codons 406 or 497. Particularly, three pairs of isolates with identical embB mutations and genotyping features were identified with variant ethambutol susceptibility. Among 77 isoniazid, rifampicin, streptomycin and ethambutol quadruple drug-resistant isolates, 89.6% carried embB mutations and 83.1% could be identified by detecting 10 embB mutations.
  
  
  CONCLUSIONS
  Our results suggest embB mutations alone are not sufficient for the development of full resistance to ethambutol in M. tuberculosis and mutations other than embB are also needed. Our study confirms the importance of mutations at embB406 and embB497 as hotspots, in addition to embB306, for detecting ethambutol resistance. Ten selected mutations of embB, covered by a short PCR product, can be used as candidate markers for the prediction of quadruple resistance to isoniazid, rifampicin, streptomycin and ethambutol.
authors.affiliation: State Key Laboratory for Molecular Virology and Genetic Engineering, Institute of Pathogen Biology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100176, China.
authors.forename: Dawei
authors.initials: D
authors.lastname: Shi
authors.forename: Liang
authors.initials: L
authors.lastname: Li
authors.forename: Yuling
authors.initials: Y
authors.lastname: Zhao
authors.forename: Qiong
authors.initials: Q
authors.lastname: Jia
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Christopher
authors.initials: C
authors.lastname: Coulter
authors.forename: Qi
authors.initials: Q
authors.lastname: Jin
authors.forename: Guofeng
authors.initials: G
authors.lastname: Zhu
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001483:Base Sequence; D002681:China; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D004977:Ethambutol / Q000494:pharmacology; D005819:Genetic Markers; D005838:Genotype; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D010430:Pentosyltransferases / Q000235:genetics*; D012293:Rifampin / Q000494:pharmacology; D017422:Sequence Analysis, DNA; D013307:Streptomycin / Q000494:pharmacology; D018088:Tuberculosis, Multidrug-Resistant / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D004269:DNA, Bacterial; D005819:Genetic Markers; D004977:Ethambutol; C540269:EmbB protein, Mycobacterium tuberculosis; D010430:Pentosyltransferases; D007538:Isoniazid; D012293:Rifampin; D013307:Streptomycin