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

PP-103
NITRATE REDUCTASE ASSAY APPLIED TO DIRECT DETECTION OF
DRUG RESISTANCE IN MYCOBACTERIUM TUBERCULOSIS.
Montoro, Ernesto 1 , Milián, Yoslaine 1 , Lemus, Dihadenys 1 , Echemendía, Miguel 1 ,
Yzquierdo, Sergio 1 , Martin, Anandi 2 , Van der Stuyft, Patrick 2 , Palomino, Juan Carlos 2
1 - Institute of Tropical Medicine Pedro Kourí (IPK), Havana, Cuba
2 - Institute of Tropical Medicine, Antwerp, Belgium
Tuberculosis still represents a major public health problem; especially in low-resource countries were the burden of the
disease is more important. Standard methods for drug susceptibility testing of Mycobacterium tuberculosis, such as the
proportional method (PM), the absolute concentration method, and the resistance ratio method, are used globally but
depend on culture on solid media and are therefore time-consuming. The time lag is a significant threat to the patient,
the community, and health care workers. To reduce this period, we have evaluated the nitrate reductase assay (NRA)
on smear-positive sputa for the direct detection of drugs resistance in Mycobacterium tuberculosis. A total of 63 smearpositive
sputum were used in this study. The samples were decontaminated using the modified Petroff method, a portion
was used to carried out the NRA as susceptibility test to isoniazid (INH, 0,2 µg/mL), streptomycin (SM, 4 µg/mL),
ethambutol (EMB, 2 µg/mL) and rifampicin (RIF, 40 µg/mL). The resulting sample was used to perform the indirect PM
on Löwenstein-Jensen which was used as gold standard method. The NRA results were obtained between 14 and 28
days. However, were necessary 28 or 42 days to obtain PM results. The sensitivity of MNR to INH, SM, EMB and RIF was
88,9%, 75%, 0% and 71,4% respectively. The low sensitivity obtained for all drug evaluated was due to a small amount of
resistance strains founded. On the other hand, the specificity of MNR to each drugs was 96,3% (INH), 96,1% (SM), 95,2%
(EMB) and 98,2% (RIF). In general, the concordance between MNR and PM was 95,2% to INH, 92,1% to SM, 93,7 to EMB
and 95,2% to RMP. In conclusion, the MNR applied in sputum samples is more rapid than any conventional method. Two
drugs that define multidrug-resistance and are the most potent in the treatment of tuberculosis, INH and RIF, showed
the higher values of concordance wit PM. The MNR results are easy to performance, use each drug with identical critical
concentration in the same solid media than PM and could be a useful tool for detection of tuberculosis drug resistance
in low-resource countries with limited laboratory facilities.
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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