A rapid test for the differentiation of Mycobacterium tuberculosis complex from non-tuberculous mycobacteria (NTM) was developed using p-nitro-benzoic acid (PNB) as inhibitor and the resazurin microplate assay (REMA) for detection of growth. One hundred and fifty-one M. tuberculosis strains and 36 NTM were evaluated. Using a cut-off of 250 µg/ml of PNB, all M. tuberculosis strains were correctly differentiated from NTM; only two NTM strains failed to be correctly identified with this procedure. The time to obtain results was 8 days compared to 28 days or more with the conventional method. The use of REMA and PNB represents a rapid and inexpensive procedure that could be used in laboratories in low-income settings for the rapid differentiation between M. tuberculosiscomplex and NTM.
Key words: Mycobacterium tuberculosis, identification, resazurin.
REMA, Resazurin microplate assay;TB, tuberculosis; NTM, non-tuberculous mycobacteria; PNB, p-nitrobenzoic acid; MGIT, mycobacterial growth indicator tube; MIC, minimal inhibitory concentration; MTT, 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide.
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