title: Genotypic Analysis of Genes Associated with Independent Resistance and Cross-Resistance to Isoniazid and Ethionamide in Mycobacterium tuberculosis Clinical Isolates.
abstract: Ethionamide (ETH) is an antibiotic used for the treatment of multidrug-resistant (MDR) tuberculosis (TB) (MDR-TB), and its use may be limited with the emergence of resistance in the Mycobacterium tuberculosis population. ETH resistance in M. tuberculosis is phenomenon independent or cross related when accompanied with isoniazid (INH) resistance. In most cases, resistance to INH and ETH is explained by mutations in the inhA promoter and in the following genes: katG, ethA, ethR, mshA, ndh, and inhA. We sequenced the above genes in 64 M. tuberculosis isolates (n = 57 ETH-resistant MDR-TB isolates; n = 3 ETH-susceptible MDR-TB isolates; and n = 4 fully susceptible isolates). Each isolate was tested for susceptibility to first- and second-line drugs using the agar proportion method. Mutations were observed in ETH-resistant MDR-TB isolates at the following rates: 100% in katG, 72% in ethA, 45.6% in mshA, 8.7% in ndh, and 33.3% in inhA or its promoter. Of the three ETH-susceptible MDR-TB isolates, all showed mutations in katG; one had a mutation in ethA, and another, in mshA and inhA. Finally, of the four fully susceptible isolates, two showed no detectable mutation in the studied genes, and two had mutations in mshA gene unrelated to the resistance. Mutations not previously reported were found in the ethA, mshA, katG, and ndh genes. The concordance between the phenotypic susceptibility testing to INH and ETH and the sequencing was 1 and 0.45, respectively. Among isolates exhibiting INH resistance, the high frequency of independent resistance and cross-resistance with ETH in the M. tuberculosis isolates suggests the need to confirm the susceptibility to ETH before considering it in the treatment of patients with MDR-TB.
authors.affiliation: Escuela de Ciencias de la Salud, Universidad Pontificia Bolivariana (UPB), Medellín, Colombia Unidad de Bacteriología y Micobacterias, Corporación para Investigaciones Biológicas (CIB), Medellín, Colombia jrueda@cib.org.co.
authors.forename: Johana
authors.initials: J
authors.lastname: Rueda
authors.affiliation: Escuela de Ciencias de la Salud, Universidad Pontificia Bolivariana (UPB), Medellín, Colombia Unidad de Bacteriología y Micobacterias, Corporación para Investigaciones Biológicas (CIB), Medellín, Colombia.
authors.forename: Teresa
authors.initials: T
authors.lastname: Realpe
authors.affiliation: Unidad de Bacteriología y Micobacterias, Corporación para Investigaciones Biológicas (CIB), Medellín, Colombia.
authors.forename: Gloria Isabel
authors.initials: GI
authors.lastname: Mejia
authors.affiliation: Unidad de Bacteriología y Micobacterias, Corporación para Investigaciones Biológicas (CIB), Medellín, Colombia.
authors.forename: Elsa
authors.initials: E
authors.lastname: Zapata
authors.affiliation: Centro Internacional de Entrenamiento e Investigaciones Médicas (CIDEIM), Cali, Colombia.
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Rozo
authors.affiliation: Centro Internacional de Entrenamiento e Investigaciones Médicas (CIDEIM), Cali, Colombia Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, Netherlands.
authors.forename: Beatriz Eugenia
authors.initials: BE
authors.lastname: Ferro
authors.affiliation: Escuela de Ciencias de la Salud, Universidad Pontificia Bolivariana (UPB), Medellín, Colombia Unidad de Bacteriología y Micobacterias, Corporación para Investigaciones Biológicas (CIB), Medellín, Colombia.
authors.forename: Jaime
authors.initials: J
authors.lastname: Robledo
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D005000:Ethionamide / Q000494:pharmacology*; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism; 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 / Q000378:metabolism; D009245:NADH Dehydrogenase / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D018088:Tuberculosis, Multidrug-Resistant / Q000188:drug therapy / Q000382:microbiology; D014397:Tuberculosis, Pulmonary / Q000188:drug therapy / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; C481661:EthR protein, Mycobacterium tuberculosis; D012097:Repressor Proteins; D036781:Fimbriae Proteins; D010088:Oxidoreductases; D002374:Catalase; C480353:katG protein, Mycobacterium tuberculosis; C085257:InhA protein, Mycobacterium; D009245:NADH Dehydrogenase; D005000:Ethionamide; D007538:Isoniazid