EVALUATION OF A NEW DETECTION METHOD OF MYCOBACTERIUM TUBERCULOSIS IN CLINICAL SPECIMENS BY AMPLIFICATION OF RIBOSOMAL RNA AND ITS CLINICAL APPLICATION

Abstract

A new rapid M. tuberculosis detection method, the Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test (MTD), which allows direct detection of M. tuberculosis in clinical specimens by amplification of M. tuberculosis ribosomal RNA (rRNA), was evaluated.
In the present study, MTD and conventional smear and culture examinations were performed on 225 sputum, 36 pleural fluid (PF), nine cerebrospinal fluid (CSF) and 41 bronchoalveolar lavage fluid (BALF) specimens.
Among 225 sputum specimens from 132 patients, 20 culture-negative specimens from 14 patients and one specimen which was culture-positive for M. fortuitum on Ogawa's egg medium were MTD-positive.
On the other hand, there were 6 M. tuberculosis culture-positive but MTD-negative specimens from 6 patients. The amount of bacilli in all six cases, however, was very few. The sensitivity of M. tuberculosis detection by MTD, as compared with Ogawa's egg me dium and MB-Check, was 93 and 92%, respectively, in sputum specimens, and the speci ficity of MTD was 80 and 85%, respectively. Taking into account not only culture positive specimens but also MTD-positive specimens from patients clinically diagnosed as active tuberculosis, the sensitivity and specificity of MTD were 93% and 99%, respectively.
Among 36 PF specimens from 31 patients, of which 20 specimens from 16 patients were clinically diagnosed as tuberculous, only 4 from 4 patients were culture-positive for M. tuberculosis while 7 from 5 patients were MTD-positive.
The results of MTD in 9 CSF specimens coincided well with those of MB-Check, but one MTD-positive specimen yielded a false-negative result with Ogawa's egg medium.
Among 41 BALF specimens from 39 patients, only one was culture-positive while one culture-positive and 7 culture-negative specimens were positive on MTD. All these MTD-positive patients were later verified as having pulmonary tuberculosis either by transbronchial lung biopsy and other examinations, or by the clinical course of the disease, particularly the response to andti-tuberculosis drugs.
Inconsistent results were seen in 21 sputum specimens from 15 patients, 4 PF specimens from 3 patients and 7 BALF specimens from 7 patients, all of which were culture-nega tive for M.tuberculosis but MTD-positive. None of these patients had any clinical findings inconsistent with diagnosis as tuberculosis.
It was noted that MTD was very useful for rapid detection of M. tuberculosis in sputum as well as other clinical specimens.
We observed the clinical course of 20 pulmonary tuberculosis patients by monthly examinations of sputum, using smears, Ogawa's egg medium, MB-Check and MTD. MTD-positivity rates fell down in parallel with decreased pulmonary tuberculous activity. During the clinical course, out of 61 MTD-negative specimens only 4 (6.6%) were culture-positive for M. tuberculosis, while out of 63 smear-and-culture-negative specimens 6 (9.5%) were MTD-positive.
These data suggest that MTD is useful to assess the clinical activity and course of tuberculosis.