| Summary: | <p>Abstract</p> <p>Background</p> <p>Ethambutol (EMB) is a first-line drug for the treatment of tuberculosis (TB). Resistance to EMB in <it>Mycobacterium tuberculosis </it>isolates is mediated by mutations in several genes involved in arabinan synthesis notably three <it>emb </it>(arabinosyl transferase) and <it>iniA </it>(isoniazid-inducible) genes. Most epidemiologically unrelated EMB-resistant <it>M. tuberculosis </it>strains contain mutations at <it>embB </it>codons 306, 406 and 497, <it>embC-embA </it>intergenic region (IGR) and <it>iniA </it>codon 501 (<it>iniA501</it>).</p> <p>Objective</p> <p>To develop a more comprehensive molecular screen for EMB-resistance detectioamong epidemiologically unrelated EMB-resistant <it>M. tuberculosis </it>strains previously analyzed for <it>embB </it>codon 306, 406 and 497 mutations by including analysis of mutations at <it>iniA501 </it>and in <it>embC-embA </it>IGR.</p> <p>Methods</p> <p>Fifty consecutive and phenotypically documented EMB-resistant and 25 pansusceptible <it>M. tuberculosis </it>strains isolated from 75 different TB patients over a four-year period in Kuwait were analyzed. Mutations at <it>iniA501 </it>were detected by PCR amplification followed by restriction fragment length polymorphism (RFLP) patterns generated with <it>Hpy </it>99 I. Direct DNA sequencing was used to confirm RFLP results and for detecting mutations in <it>embC-embA </it>IGR.</p> <p>Results</p> <p>Nearly same number of EMB-resistant <it>M. tuberculosis </it>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 <it>iniA501 </it>and in <it>embC-embA </it>IGR. The analysis of 50 EMB-resistant <it>M. tuberculosis </it>isolates showed that only one strain contained a mutated <it>iniA501 </it>while no mutation was detected in <it>embC-embA </it>IGR in any of the isolate.</p> <p>Conclusion</p> <p>Analysis of <it>iniA501 </it>and <it>embC-embA </it>IGR in epidemiologically unrelated EMB-resistant <it>M. tuberculosis </it>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.</p>
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