Utility of a Mycobacterium tuberculosis GC-rich repetitive sequence in the diagnosis of tuberculous pleural effusion by PCR

A GC-rich repetitive sequence (GCRS) of Mycobacterium tuberculosis was identified in our laboratory which displayed a high homology with GC-rich sequences of M. tuberculosis and M. bovis. A PCR assay based on the amplification of the proximal 150 bp of GCRS and its detection by non-radioactive hybridization was developed. The accuracy of the GCRS-based PCR assay was evaluated in a clinical setting for the detection of mycobacterial DNA in pleural fluids for the diagnosis of tuberculosis (TB) using clinical criteria and pleural biopsy histology as gold standard. In a blind study, a total of 67 pleural fluid samples (38 tuberculous and 29 nontuberculous) were analysed by PCR and the results were compared with pleural biopsy, Ziehl-Neelsen staining and culture. Mycobacteria could not be detected by either smear or culture techniques in any of the pleural fluids samples. Out of 38 tuberculous pleural effusions, 24 were positive by PCR (63.2% sensitivity). When PCR results were compared with pleural biopsy histology, an increased sensitivity of 73.3% was obtained. Out of the 29 nontuberculous pleural effusions, 2 false positive results were obtained accounting for an overall specificity of 93.1%. The GCRS-based PCR assay thus has a definite role in the diagnosis of tuberculous pleural effusion in contrast to smear and/or culture techniques