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 ... -  《-》

Ethionamide cross- and co-resistance in children with isoniazid-resistant tuberculosis.

Schaaf HS ，Victor TC ，Venter A ，Brittle W ，Jordaan AM ，Hesseling AC ，Marais BJ ，van Helden PD ，Donald PR ... -  《-》

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 ... -  《-》

Investigation of isoniazid and ethionamide cross-resistance by whole genome sequencing and association with poor treatment outcomes of multidrug-resistant tuberculosis patients in South Africa.

Ethionamide (ETH) and isoniazid (INH) are part of the backbone regimen used for the treatment of multidrug-resistant tuberculosis (MDR-TB). Both ETH and INH are structurally similar and are activated by ethA and katG gene products. Resistance to INH among MDR-TB patients may cause ETH to be ineffective, as both target nicotinamide adenine dinucleotide-dependent enoyl-acyl carrier protein reductase inhA protein and mutations within inhA gene may lead to their cross-resistance. Furthermore, ETH resistance is caused by mutations within ethA and ethR genes forming part of the ETH drug activation pathway. Nicotinamide adenine dinucleotide is coded by the ndh gene, and its overexpresion may lead cross-resistance between INH and ETH drugs. Phenotypic drug susceptibility testing of ETH is difficult and often unreliable. We used whole genome sequencing to compare inhA, inhA promoter, ethA, ethR ndh, and katG genetic regions in serial isolates (baseline and follow-up) with treatment outcomes. MDR-TB strains were collected from 46 patients before and during second-line drug treatment in KwaZulu-Natal and Eastern Cape between 2005 and 2009. All patients had phenotypically determined MDR-TB at baseline and had treatment outcomes documented. Unfavorable treatment outcomes were defined as death, default, and failure, while favorable outcomes were cure and treatment completion. Each strain had baseline and at least one strain collected on follow-up. From each strain, DNA was extracted from colonies grown on Löwenstein-Jensen slants, and fragment and jumping paired-end Illumina DNA libraries were constructed and sequenced on the Illumina HiSeq 2000 (Broad Institute, Cambridge, MA, USA). Sequences were aligned to H37Rv genome and Pilon was run to generate a list of SNPs. In silico spoligotyping was performed to a database 43 unique spacer sequences. Cross-resistance was defined as the presence of both inhA and either ethA or ethR mutations in clinical isolates. A total of 92 sequences from 46 serial isolates of MDR-TB patients from KwaZulu-Natal (29 isolates) and Eastern Cape (17 isolates) were analyzed. Most patients (29/46; 63.0%) had unfavorable outcomes, 13 (28.3%) had favorable outcomes, while four (8.7%) had unknown outcomes. Phylogenetic reconstruction revealed that primary genotype differed by province. The Beijing genotype was predominant in Eastern Cape, while EuroAmerican lineage (S, T, LAM, X) was found in KwaZulu-Natal. Whole genome analysis revealed nonsynonymous insertions and deletions within katG, ethA, ethR, ndh, and inhA and its promoter region. Among patients with treatment outcome data, mutations were detected in 92.8% in katG, 50% in inhA, 53.6% in ethA, 2.4% in ethR, and 19% in ndh. The majority of mutations causing ETH (20/29; 68.9%) and INH (18/29; 62.1%) resistance occurred among patients with unfavorable outcomes. Both inhA and either ethA or ethR mutations were detected in 16/29 (55.2%) patients with unfavorable outcomes. Cross-resistance of both INH and ETH drugs was associated with unfavorable treatment outcomes (p=0.021) in 16/29 (55.2%) patients compared with favorable treatment outcomes in 2/13 (15.4%) patients. Baseline ETH molecular resistance before second-line treatment is a concern. Unfavorable treatment outcomes of patients with ethA, ethR, and inhA mutations highlight the importance of genotypic testing before initiation of treatment containing ETH. The clinical significance of whole genome analysis for early detection of mutations predictive of treatment failure needs further investigation.

Malinga L ，Brand J ，Jansen van Rensburg C ，Cassell G ，van der Walt M ... -  《-》

Genotypic analysis of genes associated with isoniazid and ethionamide resistance in MDR-TB isolates from Thailand.

Boonaiam S ，Chaiprasert A ，Prammananan T ，Leechawengwongs M ... -  《-》