European Journal of Molecular & Clinical Medicine

Abstract

Mutations in embB306 are the most common polymorphisms linked with ethambutol
(EMB) resistance, accounting for 40-60% of EMB resistant tuberculosis clinical cases
(TB). The current investigation looked for further mutations linked with EMB
resistance in the embB, embC, embA, and Rv3806c (ubiA) genes in 29 EMB resistant
and 29 EMB susceptible clinical isolates of M. tuberculosis from 360 TB patients.DNA
sequencing was used to screen for polymorphisms in the entire ubiA gene, mutational
hotspot regions of embB, embC, and the upstream region of embA, and the results were
correlated with minimum inhibitory concentrations (MIC) of EMB. The most common
polymorphism in ubiA was at codon 149 (GAA to GAC), which was found in 5/29
(17.2%) resistant isolates and 7/29 (24%) susceptible isolates. Mutations in embB were
most common at codon 306 (ATG to ATC/GTG), and were found only in EMB resistant
isolates (20/29; 69%).Mutations in the upstream region of embA at -8, -11, -12, and -60
codons were also found in EMB resistant organisms (8/29; 27.5 percent), with 6/8 (75
percent) occurring in isolates with an EMB MIC of 16 g/ml. Although no
polymorphisms in ubiA were found to be related with EMB resistance, polymorphisms
upstream of embA may contribute to high levels of EMB resistance.