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Antimicrobial Agents and Chemotherapy, Aug 1997, 1677-1681, Vol 41, No. 8
S Sreevatsan, KE Stockbauer, X Pan, BN Kreiswirth, SL Moghazeh, WR Jacobs Jr, A Telenti and JM Musser
Ethambutol [(S,S')-2,2'-(ethylenediimino)di-1-butanol; EMB], is a first-
line drug used to treat tuberculosis. To gain insight into the molecular
basis of EMB resistance, we characterized the 10-kb embCAB locus in 16
EMB-resistant and 3 EMB-susceptible genetically distinct Mycobacterium
tuberculosis strains from diverse localities by automated DNA sequencing
and single-stranded conformation polymorphism analysis. All 19 organisms
had virtually identical sequences for the entire 10-kb region. Eight
EMB-resistant organisms had mutations located in codon 306 of embB that
resulted in the replacement of the wild-type Met residue with Ile or Val.
Automated sequence analysis of the 5' region (1,892 bp) of embB in an
additional 69 EMB-resistant and 30 EMB- susceptible M. tuberculosis
isolates from diverse geographic localities and representing 70 distinct
IS6110 fingerprints confirmed the unique association of substitutions in
amino acid residue 306 of EmbB with EMB resistance. Six other embB
nucleotide substitutions resulting in four amino acid replacements were
uniquely found in resistant strains. Sixty- nine percent of
epidemiologically unassociated EMB-resistant organisms had an amino acid
substitution not found in susceptible strains, and most (89%) replacements
occurred at amino acid residue 306 of EmbB. For strains with the Met306Leu
or Met306Val replacements EMB MICs were generally higher (40 microg/ml)
than those for organisms with Met306Ile substitutions (20 microg/ml). The
data are consistent with the idea that amino acid substitutions in EmbB
alter the drug-protein interaction and thereby cause EMB resistance.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Ethambutol resistance in Mycobacterium tuberculosis: critical role of embB mutations
Department of Pathology, Baylor College of Medicine, Houston, Texas 77030, USA.
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