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

PP-90
DIRECT DETECTION OF RIFAMPIN RESISTANCE IN
Mycobacterium tuberculosis BY THE NITRATE
REDUCTASE ASSAY APPLIED DIRECTLY IN SPUTUM SAMPLES
Regina Ferro e Silva 1 , Maria de Lourdes Shikama 1 , Gleize Villela 1 , Daisy Nakamura Sato 1 , Carmen
Maria Saraiva Giampaglia 1 , Maria Conceição Martins 1 , Anandi Martin 2 , Juan Carlos Palomino 2
1 - Instituto Adolfo Lutz (IAL), São Paulo, Brazil
2 - Institut of Tropical Medicine, Antwerpen, Belgium
Resistance to rifampin (RIF) is an important predictor for the early diagnosis of MDRTB. Conventional methods for
DST of M. tuberculosis require several weeks to give results.Thus, an alternative in vitro method which can detect drug
susceptibility directly from sputum and presents quick results and low cost, will be very useful for tuberculosis diagnosis.
The nitrate reductase assay uses the detection of nitrite as an indication of growth when used as a drug susceptibility test.
Objective:to compare the nitrate reductase assay (NRA) with the proportion method (PM), considered as gold standard,
to detect RIF resistance in M. tuberculosis directly from sputum samples. Method: the study was carried out by 4 regional
laboratories from the state of São Paulo, Brazil. A total of 206 sputum samples tested smear positive from patients with
pulmonary tuberculosis. The sputum was decontaminated by Petroff method and DST to RIF was carried out using the
PM and the NRA. Nitrate Reductase Assay: Sputum samples, after decontamination were inoculated in one tube control
(without drug) and one tube containing 40 µg/ml of rifampicin. Findings: the results of the DST obtained directly from
sputum were: 6 samples resistant to RIF and 200 samples susceptible. The comparison between NRA and the traditional
gold standard method showed agreement of 100%. The sensitivity and specificity of the NRA for rifampicin was 100%.
Results were available in 10 days for 66 (34%) samples, 15 days for 102 (53%) samples and 20 days for 24 (13%) samples
while the results of PM took 30 days to be available. Conclusions: the NRA proved to be a promising method for the
screening of suspect MDRTB cases directly from sputum samples. The simplicity of the method, its low cost and celerity
to give the results make it a good alternative method for laboratories in resource-poor settings.
162 ESM 2009