Early diagnosis of MDR-TB cases directly on sputum specimens by rapid molecular method

Abstract

The control of tuberculosis infection has now become more complicated due to the emergence of multidrug
resistant TB (MDR-TB). It takes a longer time of at least 6-8 weeks for diagnosis of MDR-TB by culture and
conventional DST. The aim of this study was to test early diagnosis of MDR-TB by rapid molecular method
directly from sputum specimens. A total of 56 smear positive sputum specimens were used for the detection of
RIF and INH resistant mutation by genotypic assay and compared with phenotypic DST from the same
specimens. Out of the 56 specimens, an interpretable result of MDR-TB (RIFr
+INHr
), were obtained from 13/53
(24.5%), by genotypic method and 14/53 (26.4%) from phenotypic method. The majority of common mutation
regions were seen in MUT3 64.3% (Ser531lue) in rpoB gene, MUT1 24.5% (Ser315Ile) in katG gene and MUT1
5.6% (Cys-15Thr) in inhA gene. Being an equally sensitive and specific method as compared to conventional
DST, and short turnaround time, this method is suitable for early diagnosis of MDR-TB, directly on smear
positive sputum specimens.