Evaluation of IS6110 as amplification target for direct tuberculosis diagnosis

We describe in the present study an evaluation of the IS61 10 repetitive el ement in the rapid diagnosis of pulmonary and extrapulmonary tuberculosis b y polymerase chain reaction (PCR). A pair of oligonucleotide primers was de signed to amplify a 201-bp DNA fragment of IS6110. The amplified DNA was de tected by ethidium bromide stained agarose gel electrophoresis and confirme d by Sal I digestion and Southern blot hybridization with a P-32-labeled pr obe. To detect the presence of amplification inhibitors, an internal contro l DNA that used the same primers as for the target sequence was added to ea ch PCR reaction. PCR results were compared with the results of acid fast st ained smears, cultures, and clinical data in 102 sputum and 41 extrapulmona ry specimens, With the exception of four samples, M. tuberculosis was detec ted by PCR in all smear-and culture-positive cases and in all smear-negativ e, culture positive cases. Additionally; PCR was able to detect 6 cases tha t were smear and culture negative but clinically strongly suspected of tube rculosis. The final PCR sensitivity and specificity were 93.1% and 95.18%, respectively. One M. tuberculosis strain isolated from a sputum was found t o lack IS6110. This study shows that (1) PCR diagnosis based on IS6110 reac hed the best sensitivity and specificity but must be considered carefully s ince some M. tuberculosis strains lack IS6110; and (2) PCR must be interpre ted in conjunction with clinical and radiological data when it is discordan t with conventional methods results.