Comparison of Conventional and Molecular Methods Used for Diagnosis of Mycobacterium Tuberculosis in Clinical Samples

Background: Tuberculosis (TB) is an important global public health issue, and drug resistance is the most important factor preventing its control. According to the World Health Organization, approximately 10.4 million new cases were reported worldwide in 2015, and 5% of those new cases were multidrug-resistant TB. The aim of our study is to identify rapid and accurate methods for detecting the presence of the Mycobacterium tuberculosis complex (MTBC) and its drug susceptibility in respiratory tract samples obtained from patients suspected of having TB. Methods: A total of 140 patient samples, including 110 sputum, 20 bronchoalveolar lavage fluid, and 10 fasting gastric aspirates were evaluated in this study. The acid-fast bacilli (AFB) detection by microscopy, BACTEC mycobacteria growth indicator tube 960 (MGIT-960) liquid culture system, Lowenstein-Jensen (LJ) solid culture method, and the GenoType MTBDRplus molecular methods were applied to all samples, and the resulting data were compared. Results: Among the clinical samples from patients suspected of having TB, 12% (16/140), 15% (21/140), 16% (23/140), and 14% (20/140) were positive by AFB detection, LJ conventional culture, MGIT-960 liquid culture, and PCR methods, respectively. Of the 23 strains identified by the MGIT-960 liquid culture method, 21 were MTBC, and 2 were non-tuberculous mycobacteria (NTM). Additionally, 20 of 23 culture-positive samples had positive PCR results and 3 of 23 culture-positive samples had negative PCR results. One MTBC-positive patient was determined to be negative by PCR. Only one patient was positive for rpoB and katG mutations. Conclusions: Molecular tests may be a complementary method for confirming a diagnosis of TB, considering that they yield same-day, high-sensitivity results. Due to the high specificity of PCR, positive results obtained by this test may be useful for early detection of TB. However, it would be appropriate to confirm negative results with culture and clinical findings.