Ethionamide cross-and co-resistance in children with isoniazid-resistant tuberculosis
BACKGROUND: Ethionamide (ETH) is a structural analogue of isoniazid (INH). Both are pro-drugs requiring activation by separate and common enzyme pathways, which could lead to co-and/or cross-resistance. OBJECTIVE: To characterise paediatric INH-resistant mycobacterial isolates to investigate the presence of ETH resistance and mutations in the katG gene and the inhA promoter region. METHODS: Forty-fi ve INH-resistant and 19 INHs usceptible Mycobacterium tuberculosis control isolates from children from the Western Cape Province, South Africa, were analysed to quantify INH minimal inhibitory concentration, test for ETH resistance and investigate mutations in the katG gene and/or inhA promoter region. RESULTS: Among 45 INH-resistant children, ETH resistance was present in 19 of 39 (49%). An inhA promoter mutation was identifi ed in 15 (33.3%); 12/14 (86%) of these isolates were also ETH-resistant. Of the 21 isolates with a katG mutation, six (29%) were ETH-resistant. No isolate had both katG and inhA promoter mutations. Nine (20%) isolates had neither inhA promoter nor katG mutations. Of 15 isolates with inhA promoter mutation, 14 (93%) displayed low-or intermediate-level INH resistance. Among the 19 INH-susceptible isolates, ETH resistance was present in 1/18 (6%) and none showed inhA or katG gene mutations. CONCLUSION: We found a high level of cross-and coresistance with ETH among INH-resistant M. tuberculosis isolates from children in this geographic area. © 2009 The Union.