Identification of Mycobacterium tuberculosis isolated from culture-negative pulmonary and extra-pulmonary samples in cases of suspected tuberculosis

Introduction: Mycobacterium tuberculosis is the cause of pulmonary and extra-pulmonary tuberculosis. Latent tuberculosis is asymptomatic and the results of mycobacterial culture in this case are negative. The purpose of this study was to determine the prevalence of M. tuberculosis in negative cultures of pulmonary and extra-pulmonary samples from suspected tuberculosis patients in Yazd city. Methods: Specimens were collected from 44 patients with suspected pulmonary and extra-pulmonary tuberculosis. The culture result of all samples was negative and DNA was extracted from culture-negative samples. Then the IS6110 sequence of M. tuberculosis was determined by PCR, and the presence of 16S rRNA and rrnA-PCL1 was checked by real-time PCR. Data were analyzed using SPSS software. Results: Of the 44 pulmonary and extra-pulmonary samples, M. tuberculosis DNA was detected in 12 cases (27%) by PCR. Of the 12 positive cases of M. tuberculosis, 9 were detected in lung samples and 3 in extra-pulmonary samples. For rrnA-PCL1 and 16S rRNA genes, 10 samples (23%) were confirmed positive by real-time PCR. The frequency distributions of M. tuberculosis according to PCR and real-time PCR were not significantly different (p=0.403). Conclusion: Latent tuberculosis is characterized by the absence of clinical symptoms and the absence of bacilli in the culture. Regardless of the statistical analysis of results, PCR more effectively detects M. tuberculosis than does real-time PCR. According to the results, detection of M. tuberculosis in pulmonary and extra-pulmonary samples with culture-negative by PCR is reliable.