Sequence-based detection of first-line and second-line drugs resistance-associated mutations in Mycobacterium tuberculosis isolates in Isfahan, Iran

Abstract

Tuberculosis is an infectious disease, which requires special medical attention due to the emergence of multi drug-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.