Application of nested polymerase chain reaction (nPCR) using MPB 64 gene primers to detect Mycobacterium tuberculosis DNA in clinical specimens from extrapulmonary tuberculosis patients.

BACKGROUND & OBJECTIVE The conventional culture technique for diagnosis of extrapulmonary tuberculosis is time consuming. In order to find a sensitive and rapid technique nested polymerase chain reaction (nPCR) targeting the conserved MPB 64 gene of Mycobacterium tuberculosis was evaluated for detection of M. tuberculosis DNA directly from clinical specimens of extrapulmonary origin. METHODS A total of 400 clinical specimens from clinically suspected cases of extrapulmonary tuberculosis and 30 control specimens of nontuberculous aetiology were processed by smear and culture and by nPCR technique for detection of M. tuberculosis. The specimens were divided into 3 groups, (group I--280 specimens [104 peritoneal fluid (PF), 120 cerebrospinal fluid (CSF), 44 lymph node biopsies 3 pericardial fluid and 9 other biopsy specimens], group II--120 aqueous humour (AH) from idiopathic granulomatous uveitis cases, and group III--30 control specimens (10 CSF and 20AH). RESULTS The conventional culture was positive only in 16 of 400 specimens. The overall positivity of nPCR was 35.2 per cent (141/400). Among the 280 specimens from extrapulmonary lesions (group I), 15 were bacteriologically positive, while 115 of 265 bacteriologically negative specimens (43.4%) were positive by nPCR. All the 30 control specimens were negative by nPCR. INTERPRETATION & CONCLUSION The nPCR using MPB64 gene primers might be a rapid and reliable diagnostic technique for detection of M. tuberculosis genome in clinically suspected extrapulmonary tuberculosis specimens, as compared to the conventional techniques.