Mutation atembBCodon 306, a Potential Marker for the Identification of Multidrug Resistance Associated with Ethambutol in Mycobacterium tuberculosis

Abstract

dEthambutol inhibits arabinogalactan and lipoarabinomannan biosynthesis in mycobacteria. The occurrence of mutations in embB codon 306 in ethambutol-susceptible isolates and their absence in resistant isolates has raised questions regarding the utility of this codon as a potential marker for resistance against ethambutol. The characterization of mutations on embB 306 will contribute to a better understanding of the mechanisms of resistance to this drug; therefore, the purpose of this study was to investigate the association between embB 306 mutations and first-line drug resistance profiles in tuberculosis isolates. We sequenced the region surrounding the embB 306 codon in 175 tuberculosis clinical isolates, divided according to drug sensitivity, in three groups: 110 were resistant to at least one first-line drug, of which 61 were resistant to ethambutol (EMB r ), 49 were sensitive to ethambutol (EMB s ) but were resistant to another drug, and 65 were pansensitive isolates (P s ). The associations between embB 306 mutations and phenotypic resistance to all first-line drugs were determined, and their validity and safety as a diagnostic marker were assessed. One of the P s isolates ( The mismanagement of patients and inadequate administration of antimicrobial therapy are the most important factors contributing to the development of drug-resistant TB (DR-TB). According to the WHO, DR-TB has become a major public health problem in several settings and, depending on the particular country, 5% of TB new cases and 20% of previously treated cases exhibit simultaneous resistance to isoniazid (INH) and rifampin (RIF) and an aggravated form of DR-TB known as multidrugresistant TB (MDR-TB) (2).Ethambutol (EMB) was introduced in 1961 as a bacteriostatic agent effective against actively growing mycobacteria. It is currently used in combination with other first-line drugs, such as INH and RIF, for the treatment of new TB cases and, depending on the resistance profile, retreatment cases (3). Resistance to EMB has been associated with acquired mutations in the emb cluster of three contiguous genes named embC, embA, and embB (4, 5). The embA and embB genes encode arabinosyl transferases involved in the arabinosylation of arabinogalactan, while embC is implicated in the arabinosylation of lipoarabinomannan (6-8).Several studies have identified mutations at codon 306 of embB as the most common alterations in EMB-resistant (EMB r ) isolates (9-20). However, the occurrence of embB codon 306 mutations in EMB-susceptible isolates (EMB s ) and the absence of mutations in EMB r isolates have raised questions regarding the utility of this codon as a potential marker for resistance (11,19,(21)(22)(23)(24). In addition, a significant increase in the proportion of MDR-TB strains bearing embB 306 mutations has recently been observed (25, 26), and 10 mutations from codons 306 to 508 of embB have been suggested as candidate markers for the prediction of quadruple resistance to INH, RIF, streptomycin (STR), and EMB (27). The identification of mu...

Association between embB Codon 306 Mutations, Phenotypic Resistance Profiles, and Genotypic Characterization in Clinical Mycobacterium tuberculosis Isolates from Hebei, China

“…The results obtained here are in line with earlier findings from Russia, where the presence of embB306 mutations in EMB-susceptible DR isolates was first described, that were confirmed by several following studies (7,8,15,16). The discrepancies between embB306 mutations and EMB resistance in our study were observed only in isolates sensitive to EMB but resistant to at least one of the other first-line drugs, and none of the pan-sensitive isolates carried mutations at embB306.…”

“…Prior studies have demonstrated a strong association between embB306 mutations and resistance to INH and RIF or MDR (8,10,11,28). In our study, embB306 mutations were found only in DR isolates, and a strong correlation between these mutations and resistance to INH and RIF and MDR was observed.…”

“…Overall, approximately 50% to 60% of EMB-resistant isolates carry a mutation in embB306 (5-7). However, discrepancies between an embB306 mutation and phenotypic EMB resistance have limited the utility of molecular assays based on the detection of an embB306 mutation for the prediction of EMB resistance (6,8,9). Prior studies have demonstrated a strong association between embB306 mutations and resistance to isoniazid (INH) or rifampin (RIF) or MDR (8, 10, 11).…”

“…However, discrepancies between an embB306 mutation and phenotypic EMB resistance have limited the utility of molecular assays based on the detection of an embB306 mutation for the prediction of EMB resistance (6,8,9). Prior studies have demonstrated a strong association between embB306 mutations and resistance to isoniazid (INH) or rifampin (RIF) or MDR (8,10,11). The identification of mutations at embB306 will contribute to a better understanding of the mechanisms of resistance to EMB and help evaluate the predictive value of this mutation for resistance to INH and RIF and MDR.…”

Draft Genome Sequence of the First Confirmed Isolate of Multidrug-Resistant Mycobacterium tuberculosis in Tasmania

“…Additional mutations were detected in the embB gene (Atg/Gtg, M306V) and pncA gene (cCg/cTg, P62L) that are associated with resistance to ethambutol and pyrazinamide, respectively ( 15 – 18 ). Furthermore, an A/C substitution was detected at position 514 of the 16S rRNA gene, rrs (MTB000019), and is related to streptomycin resistance ( 19 , 20 ).…”