Detection of novel mutations associated with independent resistance and cross-resistance to isoniazid and prothionamide in Mycobacterium tuberculosis clinical isolates.

Prothionamide, a structural analogue of isoniazid, is used mainly for treating multidrug-resistant tuberculosis (MDR-TB). Both drugs have a common target InhA, so prothionamide can be ineffective against isoniazid-resistant (INHR) Mycobacterium tuberculosis. We aimed to investigate the prevalence of mutations in katG, ethA, ndh, ethR, mshA, inhA and/or its promoter associated with independent resistance and cross-resistance to INHR and/or prothionamide-resistant (PTOR) M. tuberculosis isolates. We sequenced the above genes in 206 M. tuberculosis isolates with susceptibility testing against ten drugs. Of the 173 INHR PTOR isolates, 170 (98.3%) harboured mutations in katG, 111 (64.2%) in ethA, 58 (33.5%) in inhA or its promoter, 5 (2.9%) in ndh, 3 (1.7 %) in ethR and 2 (1.2%) in mshA. Among the 18 INHR PTOS isolates, mutations in katG were found in all of them; one had a mutation in the inhA promoter and another in ndh. Of the five INHS PTOR isolates, four showed mutations in ethA and two in the inhA promoter. Notably, 55 novel non-synonymous mutations were found in them and 20.2% of the PTORM. tuberculosis isolates harboured no known mutations. This is the first report to investigate cross-resistance between INHR and/or PTOR isolates. Among INHR (94.4% MDR-TB) M. tuberculosis isolates, the high diversity of mutations for independent resistance and cross-resistance with prothionamide highlight the importance of both phenotypic susceptibility and genotypic diagnosis when using it to treat patients with INHR-TB. The high proportion (one-fifth) of PTORM. tuberculosis isolates showed no known mutation related to PTOR genes, so uncovered resistance mechanism(s) of prothionamide exist.

Islam MM ，Tan Y ，Hameed HMA ，Liu Z ，Chhotaray C ，Liu Y ，Lu Z ，Cai X ，Tang Y ，Gao Y ，Surineni G ，Li X ，Tan S ，Guo L ，Cai X ，Yew WW ，Liu J ，Zhong N ，Zhang T ... -  《-》

Genotypic Analysis of Genes Associated with Independent Resistance and Cross-Resistance to Isoniazid and Ethionamide in Mycobacterium tuberculosis Clinical Isolates.

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.

Rueda J ，Realpe T ，Mejia GI ，Zapata E ，Rozo JC ，Ferro BE ，Robledo J ... -  《-》

Detection of mutations associated with isoniazid resistance in multidrug-resistant Mycobacterium tuberculosis clinical isolates.

To determine the prevalence of isoniazid resistance-conferring mutations among multidrug-resistant (MDR) isolates of Mycobacterium tuberculosis from Poland. Nine genetic loci, including structural genes (katG, inhA, ahpC, kasA, ndh, nat and mshA) and regulatory regions (i.e. the mabA-inhA promoter and oxyR-ahpC intergenic region) of 50 MDR M. tuberculosis isolates collected throughout Poland were PCR-amplified in their entirety and screened for mutations by direct sequencing methodology. Forty-six (92%) MDR M. tuberculosis isolates had mutations in the katG gene, and the katG Ser315Thr substitution predominated (72%). Eight (16%) isolates (six with a mutated katG allele) had mutations in the inhA promoter region and two such isolates also had single inhA structural gene mutations. Mutations in the oxyR-ahpC locus were found in five (10%) isolates, of which all but one had at least one additional mutation in katG. Mutations in the remaining genetic loci (kasA, ndh, nat and mshA) were detected in 12 (24%), 4 (8%), 5 (10%) and 17 (34%) MDR isolates, respectively. All non-synonymous mutants for these genes harboured mutations in katG. One isolate had no mutations in any of the analysed loci. This study accentuates the usefulness of katG and inhA promoter mutations as predictive markers of isoniazid resistance. Testing only for katG 315 and inhA -15 mutations would detect isoniazid resistance in 84% of the MDR M. tuberculosis sample. This percentage would increase to 96% if the sequence analysis was extended to the entire katG gene. Analysis of the remaining genetic loci did not contribute greatly to the identification of isoniazid resistance.

Jagielski T ，Bakuła Z ，Roeske K ，Kamiński M ，Napiórkowska A ，Augustynowicz-Kopeć E ，Zwolska Z ，Bielecki J ... -  《-》

The impact of combined gene mutations in inhA and ahpC genes on high levels of isoniazid resistance amongst katG non-315 in multidrug-resistant tuberculosis isolates from China.

Liu L ，Jiang F ，Chen L ，Zhao B ，Dong J ，Sun L ，Zhu Y ，Liu B ，Zhou Y ，Yang J ，Zhao Y ，Jin Q ，Zhang X ... -  《-》

Prevalence of isoniazid resistance-conferring mutations associated with multidrug-resistant tuberculosis in Free State Province, South Africa.

Pitso L ，Potgieter S ，Van der Spoel van Dijk A 《-》