Revalidation of smear negative tubercular infection by conventional and by PCR applications

Author(s): Kanchan Srivastava, Dinesh K. Tripathi, Kishore K. Srivastava, Surya Kant*

Abstract

IS6110 sequence based Polymerase Chain reaction (PCR) was compared with conventional bacteriological techniques in the laboratory diagnosis of Mycobacterium tuberculosis (MTB). A retrospective study involving one hundred and twenty six, non-repeated clinical isolates patients being investigated for tuberculosis. The samples were also processed for Ziehl-Neelsen (ZN) staining for acid fast bacilli (AFB) and culture for MTB. All the samples were processed for PCR amplification with primer targeting 123 bp fragments of insertion sequences IS6110 of M. tuberculosis complex (MTC) and the sensitivity of PCR was analyzed. Of the 126 patients, 100% and 97.3% were smears and culture positive for MTB respectively. Using culture as the gold standard, the overall sensitivity of PCR was 97.62%, and for either positive or either negative clinical isolates it was 97.06%% and 92.31%, respectively. The current study evaluated a PCR assay for the detection of MTC strains by targeting the IS6110 insertion element. This PCR has emerged as a rapid, reliable and a potent tool in establishing the diagnosis of tuberculosis with higher sensitivity than ZN microscopy and greater alacrity than culture.

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