Association between embB Codon 306 Mutations, Phenotypic Resistance Profiles, and Genotypic Characterization in...

Ethambutol (EMB) is an essential first-line drug for tuberculosis (TB) treatment. Nucleotide substitutions at embB codon 306 (embB306) have been proposed to be a potential marker for EMB resistance and a predictor of broad drug resistance in clinical Mycobacterium tuberculosis isolates. However, discordant findings about the association between embB306 mutations and EMB resistance were reported. Hebei Province is located in the Beijing-Tianjin-Hebei integration region in China; however, little information about the genetic diversity of the embB locus in this area is available. In this study, we sequenced the region surrounding embB306 (codons 207 to 445) in 62 ethambutol-resistant (EMB^r) isolates, 214 ethambutol-susceptible isolates resistant to other first-line drugs (EMB^s isolates), and 100 pan-sensitive isolates. Our data indicated that none of the pan-sensitive isolates showed mutations at embB306 and 63 drug-resistant isolates harbored embB306 substitutions, with these substitutions being found in 56.5% (35/62) of EMB^r isolates and 13.1% (28/214) of EMB^s isolates. A significant association between the embB306 mutation and resistance to isoniazid, rifampin, EMB, and multiple drugs was observed, and the rate of mutation of embB306 increased with increasing numbers of first-line drugs to which the isolates were resistant. The embB306 mutation is not the sole causative factor for EMB resistance, and the poor sensitivity limits its utility as a marker for drug-resistant TB. However, it may be a potential marker for broad drug resistance, especially for multidrug resistance. The mycobacterial interspersed repetitive unit-variable-number tandem-repeat profiles may serve as markers for predicting the embB306 substitutions that may occur in drug-resistant M. tuberculosis isolates under antimicrobial selection pressure.