The demonstration of tuberculosis using molecular genetic methods polymerase chain reaction (PCR) and Amplified Mycobacterium tuberculosis direct (AMTD) test
Abstract
Introduction: Tuberculosis is a communicable disease, in most instances with a chronic course. The aetiological agent is Mycobacterium tuberculosis.
Its demonstration is based on microscopic investigations and cultures. Microscopy is not sufficiently sensitive, while cultures are lengthy.
One of the possibilities of speeding up diagnosis are molecular genetic methods. Purpose of the study: To compare the demonstration of mycobacteria using molecular genetic methods with the results of cultures.
Methods: We used two methods to demonstrate the nucleic acid complex of Mycobacterium tuberculosis - the polymerase chain reaction (PCR) and the Amplified Mycobacterium tuberculosis direct test (AMTD). We investigated 647 samples.
Out of these, 275 samples were tested with PCR and 372 were investigated with a AMTD set. At the same time we started for each sample a parallel culture.
Results: In 275 samples, out of a total of 647, which were analysed with PCR, mycobacterial DNA was demonstrated in 18 (6.5 %). Out of the 372 samples investigated with AMTD, mycobacterial RNA was demonstrated in 27 (7 %).
Out of the 18 PRC positive samples, 6 (13 %) did not yield a positive mycobacterial culture. Out of the 27 positive results RNA with the AMTD method 17 did not yield positive cultures.
On the other hand, a diagnosis of tuberculosis verified by cultures without a positive PCR was found in 2 patients (0.7 %). Diságreement between the results of AMTD and cultures was also found in 2 samples (0.5 %).
Conclusions: Molecular genetic methods substantially speed up the diagnosis of tuberculosis. These methods are particularly important in cases of paucibacillary material and of unique and unrepeatable samples (tissues biopsies, nodes, cerebrospinal fluid).
Given the possibility of false positive results, parallel verification by microscopy and cultures is essential.