Sequence-based detection of first-line and second-line drugs resistance-associated mutations in Mycobacterium tuberculosis isolates in Isfahan, Iran.
Tuberculosis is an infectious disease, which requires special medical attention due to the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains. The present study aimed to assess drug resistance to first-line anti-mycobacterial drugs, including rifampin (RIF), isoniazid (INH), and ethambutol (EMB), as well as second-line drugs, including ofloxacin (OFX), kanamycin (KAN), amikacin (AMK), and capreomycin (CAP). The following eight loci were investigated to evaluate drug resistance: rpoB, katG, inhA, and embB, associated with resistance to RIF, INH, and EMB and gyrA, rrs, eis, and tlyA, associated with resistance to OFX, AMK, KAN, and CAP. A total of 482 patients with tuberculosis, who were referred to Molla Haadi Sabzevari Healthcare Center (Isfahan, Iran) during 2014-2017, were studied. Of 482 patients with tuberculosis, 32 (6.63%) Mycobacterium tuberculosis isolates were resistant to the first-line anti-mycobacterial drugs. Overall, 23 (71.8%), 13 (40.6%), and 3 (9.3%) isolates were resistant to INH, RIF, and EMB, respectively. Also, 13 (100%), 6 (46.1%), and 1 (7.6%) out of 13 MDR/RIF-resistant isolates were resistant to CAP and KAN, AMK, and OFX, respectively. Among the eight loci, non-synonymous substitutions were observed in rpoB (n = 7), katG (n = 10), inhA (n = 7), gyrA (n = 13), and rrs (n = 3), whereas synonymous substitutions were seen in tlyA and gyrA. On the other hand, no mutation was detected in embB or eis. Based on the present results, mutations in the eis promoter region and embB locus may not be involved in resistance to KAN and EMB in our study population. Also, the gyrA Asp94Asn mutation may be an indicator of resistance to OFX. We did not detect any XDR isolates, whereas MDR and pre-XDR isolates were found, which can be alarming.
Safari M
，Moghim S
，Salehi M
，Jafari R
，Nasr Esfahani B
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Characterisation of drug resistance-associated mutations among clinical multidrug-resistant Mycobacterium tuberculosis isolates from Hebei Province, China.
Multidrug-resistant tuberculosis (MDR-TB) is a major public-health problem in China. However, there is little information on the molecular characterisation of clinical MDR-TB isolates in Hebei Province.
In this study, 123 MDR-TB isolates were identified in sputum cultures using traditional drug susceptibility testing. The isolates were analysed for mutations in seven genes associated with resistance to antituberculous four drugs: katG and inhA promoter for isoniazid (INH); rpoB for rifampicin (RIF); gyrA and gyrB for ofloxacin (OFLX); and rrs and eis promoter for kanamycin (KAN). All strains were genotyped by spoligotyping and 15-loci MIRU-VNTR analysis.
A total of 39 distinct mutations were found at the seven loci in 114/123 (92.7%) MDR-TB isolates. Frequencies of INH, RIF, OFLX and KAN resistance-associated mutations were 82.1% (101/123), 83.7% (103/123), 92.1% (35/38) and 76.2% (16/21), respectively. The most prevalent mutations involved in resistance were: Ser315Thr in katG (70/123; 56.9%) and C(-15)T in inhA (15/123; 12.2%) for INH; Ser531Leu in rpoB (72/123; 58.5%) for RIF; Asp94Gly in gyrA (10/38; 26.3%) for OFLX; and A1401G in rrs (12/21; 57.1%) for KAN. Four novel gyrB mutants (Leu442Leu, Ser447Phe, Asn499Thr and Ala504Val) were identified. Mutations in katG, rpoB (or both) and the inhA promoter showed a sensitivity of 75.6% and specificity of 97.0% for detection of MDR-TB. DNA sequencing of the seven loci was 57.1% sensitive and 91.0% specific for prediction of XDR-TB isolates.
These results may be of value in rapid molecular detection of MDR- and XDR-TB isolates in clinical samples in Hebei Province.
Li Q
，Wang Y
，Li Y
，Gao H
，Zhang Z
，Feng F
，Dai E
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