Multicentre study of nitrate reductase assay for rapid detection of rifampicin-resistant M. tuberculosis.
METHODS
Four regional laboratories belonging to the Mycobacteria Reference Laboratory of São Paulo State, Brazil.


OBJECTIVE
To evaluate the nitrate reductase assay (NRA) for rifampicin (RMP) susceptibility testing of Mycobacterium tuberculosis directly from clinical sputum samples of patients with pulmonary tuberculosis (TB).


METHODS
Performance of the NRA for detection of M.tuberculosis susceptibility to RMP was evaluated with 210 clinical sputum samples received by the participating laboratories during 2005 and 2006 and compared with the results of the direct proportion method.


RESULTS
Susceptibility tests performed using the NRA and the direct proportion method showed 204 susceptible isolates and six isolates resistant to RMP by both methods. NRA sensitivity and specificity for RMP was 100%. The NRA results of susceptibility tests against RMP were available in 15 days for 87% of the samples. The results showed that NRA may yield a rapid answer in determining resistance for the majority of sputum samples with smear results reported as 3+ and 2+.


CONCLUSIONS
The results demonstrate the feasibility of NRA for screening resistant strains in sputum samples from patients with pulmonary TB. NRA represents a rapid and low-cost alternative method that might be used in microbiological laboratories where resources are scarce.
Shikama
M L
ML
Department of Bacteriology, Instituto Adolfo Lutz, Sorocaba, São Paulo, Brazil.
Ferro e Silva
R
R
Villela
G
G
Sato
D N
DN
Martins
M C
MC
Giampaglia
C M S
CM
da Silva
R F A M
RF
Ferro e Silva
P
P
da Silva Telles
M A
MA
Martin
A
A
Palomino
J C
JC
D000904:Antibiotics, Antitubercular / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000187:drug effects; D050901:Nitrate Reductase / Q000032:analysis*; D011933:Reagent Kits, Diagnostic; D012293:Rifampin / Q000494:pharmacology*; D013183:Sputum / Q000382:microbiology*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis / Q000382:microbiology*
D000904:Antibiotics, Antitubercular; D001426:Bacterial Proteins; D011933:Reagent Kits, Diagnostic; D050901:Nitrate Reductase; D012293:Rifampin