STUDY OF PHENOTYPIC AND MOLECULAR CHARACTERIZATION OF MYCOBACTERIUM TUBERCULOSIS ISOLATES RESISTANT TO BOTH ISONIAZID AND ETHAMBUTOL

Abstract

In the present study, we performed radiometric susceptibility testing, and we analyzed the genetic regions associated with resistance to isoniazid (INH) and ethambutol (EMB) in 100 selected isolates of Mycobacterium tuberculosis by polymerase chain reaction (PCR). The studied codons of M. tuberculosis were amino acid Ser315 of katG for INH resistance and embB Met306 and Gly406 for EMB resistance. The goal of the study was to determine (1) how often these common mutations occurred in the targeted genes in isolates displaying resistance in the phenotypic assays, (2) whether the particular INH-resistance-associated mutation occurred with the studied particular EMB-resistance-associated mutation and (3) the value of PCR to these regions as a rapid screening tool to identify multidrug-resistant (MDR) M. tuberculosis. The percentage of isolates resistant to INH, rifampicin (RIF), EMB and streptomycin (STR) was 70, 20, 100 and 70%, respectively. All resistant strains of M. tuberculosis to INH, RIF and STR were resistant to EMB. Sixty strains (85.7%) with phenotypic resistance to INH displayed mutation in amino acid Ser315 of katG sequence. All strains resistant (100%) to EMB had mutations in amino acids Met306 and Gly406 of embB sequence. In conclusion, both mutations in amino acid Ser315 of katG for INH resistance and embB Met306 and Gly406 for EMB resistance are common findings in MDR-M. tuberculosis. Moreover, the study of embB Met306 and Gly406 for EMB resistance by PCR can be used as a rapid screening test for identifying MDR-M. tuberculosis.