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Background  Ethambutol (EMB) is a first-line drug for the treatment of tuberculosis (TB). Resistance to EMB in  Mycobacterium tuberculosis  isolates is mediated by mutations in several genes involved in arabinan synthesis notably three  emb  (arabinosyl transferase) and  iniA  (isoniazid-inducible) genes. Most epidemiologically unrelated EMB-resistant  M. tuberculosis  strains contain mutations at  embB  codons 306, 406 and 497,  embC-embA  intergenic region (IGR) and  iniA  codon 501 ( iniA501 ).    Objective  To develop a more comprehensive molecular screen for EMB-resistance detectioamong epidemiologically unrelated EMB-resistant  M. tuberculosis  strains previously analyzed for  embB  codon 306, 406 and 497 mutations by including analysis of mutations at  iniA501  and in  embC-embA  IGR.    Methods  Fifty consecutive and phenotypically documented EMB-resistant and 25 pansusceptible  M. tuberculosis  strains isolated from 75 different TB patients over a four-year period in Kuwait were analyzed. Mutations at  iniA501  were detected by PCR amplification followed by restriction fragment length polymorphism (RFLP) patterns generated with  Hpy  99 I. Direct DNA sequencing was used to confirm RFLP results and for detecting mutations in  embC-embA  IGR.    Results  Nearly same number of EMB-resistant  M. tuberculosis  strains were resistant to EMB alone and EMB together with additional resistance to rifampicin and isoniazid (9 of 50, 18% and 11 of 50, 22%, respectively). All the 25 pansusceptible strains contained wild-type sequences at  iniA501  and in  embC-embA  IGR. The analysis of 50 EMB-resistant  M. tuberculosis  isolates showed that only one strain contained a mutated  iniA501  while no mutation was detected in  embC-embA  IGR in any of the isolate.    Conclusion  Analysis of  iniA501  and  embC-embA  IGR in epidemiologically unrelated EMB-resistant  M. tuberculosis  isolates in Kuwait indicate that mutations at these locations occur very infrequently and their inclusion for the development of a comprehensive molecular screen will make only minor contribution towards rapid EMB resistance detection.

annals of clinical microbiology and antimicrobials

Minor contribution of mutations at iniA codon 501 and embC-embA intergenic region in ethambutol-resistant clinical Mycobacterium tuberculosis isolates in Kuwait