How a PCR Sequencing Strategy Can Bring New Data to Improve the Diagnosis of Ethionamide Resistance

Abstract

Ethionamide (ETH) is a second-line antituberculosis drug. ETH resistance (ETH-R) is mainly related to the mutations of the monooxygenase-activating ETH (EthA), the ETH target (InhA), and the inhA promoter. Nonetheless, diagnosing ETH-R is still challenging. We assessed the strategy used for detecting ETH-R at the French National Reference Center for Mycobacteria in 497 MDR-TB isolates received from 2008 to 2016. The genotypic ETH’s resistance detection was performed by sequencing ethA, ethR, the ethA-ethR intergenic region, and the inhA promoter in the 497 multidrug-resistant isolates, whereas the phenotypic ETH susceptibility testing (PST) was performed using the reference proportion method. Mutations were found in up to 76% of the 387 resistant isolates and in up to 28% of the 110 susceptible isolates. Our results do not support the role of ethR mutations in ETH resistance. Altogether, the positive predictive value of our genotypic strategy to diagnose ETH-R was improved when only considering the variants included in the WHO catalogue and in other databases, such as TB-Profiler. Therefore, our work will help to update the list of mutations that could be graded as being associated with resistance to improve ETH-R diagnosis.

Detection of Mutations and Genotyping of Drug-Resistant Mycobacterium Tuberculosis Strains Isolated From Patients in Rural Eastern Cape Province

“…This suggests that mutation of the inhA gene does not always indicate a low resistance level. Due to the common target of action, mutations in the inhA gene also confer cross-resistance to ethionamide (ETH), a second-line drug used in MDR therapy, and thus considered as a surrogate marker for early detection of ETH resistance [8,39,40]. Previously, the National Department of Health (NDoH) in South Africa included ETH in the treatment regimen for MDR-TB in South Africa.…”

“…According to van Soolingen et al [52] Beijing lineage was described for the first time in East Asian countries with a specific spoligotype pattern characterized by the presence of the last 10 spacers (spacers [34][35][36][37][38][39][40][41][42][43]. Historical evidence supported by genetic data established that the Beijing strains were historically recently brought to South Africa, not directly from its primary origin (China), but from the secondary one (Indonesia) [46].…”

Genetic Characterization Conferred Co-Resistance to Isoniazid and Ethionamide in Mycobacterium tuberculosis Isolates from Southern Xinjiang, China

“…Imperfectly, for the ETH resistance prediction, we found an optimal combination of ethA, inhA and its promoter and ndh by WGS showed sensitivity of 61.76 and specificity of 76.62%; the sensitivity was lower than the findings from France (78.6%) 53 and Colombia (84.2%), 37 and a possible explanation was that the isolates resistant to ETH (n = 34) collected in our study were relatively small so that limited the detection of the variety of gene variations. The sensitivity and specificity for detecting cross-resistance between INH and ETH by WGS of the combination of inhA and its promoter and ndh were 48.00% and 97.65%, respectively, which was the same as other findings.…”

The Detection of Mutations and Genotyping of Drug-Resistant Mycobacterium tuberculosis Strains Isolated from Patients in the Rural Eastern Cape Province

“…This suggests that mutation of the inhA gene does not always indicate a low resistance level. Mutations in the inhA gene also give rise to cross-resistance to ethionamide (ETH), a second-line medication used in MDR therapy, and are therefore thought of as a surrogate marker for early diagnosis of ETH resistance [ 10 , 47 , 48 ]. This is because the two drugs share the same target of action.…”