European Society of Mycobacteriology - Instituto Nacional de Saúde ...

DETECTION OF EMBB GENE CODON 306 MUTATIONS IN ETHAMBUTOL
SUSCEPTIBLE AND RESISTANT Mycobacterium tuberculosis STRAINS.
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Montoro, Ernesto 1 ; Yzquierdo, Sergio 1 ; Lemus, Dihadenys 1 ; Echemendia, Miguel 1 ; Takiff, Howard 2
1 - Institute of Tropical Medicine Pedro Kourí (IPK), Havana, Cuba
2 - Venezuelan Institute for Scientific Research (IVIC), Caracas, Venezuela
Ethambutol (EMB) is one of the first line drugs in the treatment of tuberculosis. The major mechanism of acquisition of
resistance to EMB in Mycobacterium tuberculosis seems to be associated with points mutations in the embCAB operon encoding
different arabinosyl transferases. In particular, amino acid replacements at embB gene codon 306 occur frequently
in EMB-resistant M. tuberculosis strains. However, this alteration has been also reported in multidrug-resistant (MDR)
strains susceptible to EMB. The aim of this work was to detect the most frequently mutation at codon 306 in EMBresistant
strains as well as MDR strains. For this purpose, the indirect Proportional Method (PM) on Löwenstein-Jensen
was carried out as susceptibility test to isoniazid (0,2 µg/mL), streptomycin (4 µg/mL), EMB (2 µg/mL) and rifampicin (40
µg/mL) on 86 M. tuberculosis strains from the collection at the National Reference Tuberculosis Laboratory. All strains
that showed resistance to EMB by PM, all MDR strains and a selection of EMB-susceptible strains were extracted the
DNA to obtain a fragment of 803 bp by PCR, corresponding to embB gene codon 306. All this fragments were sequenced
by automatic form using appropriate primers and they data were assembled, edited electronically, and compared with
wildtype gene sequences. From 34 MDR strains, only 18 showed mutations (53%) being 8 resistant and 10 susceptible
strains to EMB. The 61,5% of EMB-resistant strains showed mutations at codon 306 whereas EMB-susceptible strains no
had alterations in this fragment. In conclusion, the results confirm that embB gene codon 306 is responsible of majority
EMB-resistant in M. tuberculosis. All mutations were founded in MDR strains and because of this, the simple detection of
changes in this fragment could be considered as multidrug-resistance marker.
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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