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Journal of Clinical Microbiology, May 1997, 1161-1165, Vol 35, No. 5
NT Jou, RB Yoshimori, GR Mason, JS Louie and MR Liebling
Several problems remain before molecular biology-based techniques, such as
PCR, are widely accepted for the detection of infectious agents. Among the
most formidable of these problems are the inability of the tests to
distinguish between viable and nonviable organisms. We approached this
problem by using the fact that bacterial mRNA has an extremely short
half-life, averaging only a few minutes. We reasoned that by targeting
bacterial mRNA by a reverse transcriptase PCR (RT- PCR), a positive signal
would indicate the presence of a recently viable organism. To test our
hypothesis, we chose to target the mRNA coding for the ubiquitous 85B
antigen of mycobacteria. After partially sequencing the gene coding for
85B, we developed primers that were specific for Mycobacterium
tuberculosis. In a single-tube, nested, RT- PCR (STN RT-PCR), these primers
detected fewer than 40 CFU in spiked sputum samples and as few as 12 CFU in
clinical sputum specimens. The sensitivity of STN RT-PCR with
smear-negative samples was as good as that of culture. The specificity was
100%. More importantly, when M. tuberculosis was cultured with and without
1 microgram of isoniazid per ml, this assay could distinguish between those
cultures which contained the antibiotic and those which did not.
Subcultures on Lowenstein- Jensen agar confirmed the viability assessments
of the STN RT-PCR. Control experiments demonstrated that isoniazid did not
inhibit the RT- PCR. In addition, when an IS6110-targeted, DNA PCR was used
to examine the same samples, all samples though 13 days (the last sample)
continued to be positive, irrespective of whether isoniazid was present,
thereby demonstrating the superiority of an mRNA target in the detection of
mycobacterial viability.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Single-tube, nested, reverse transcriptase PCR for detection of viable Mycobacterium tuberculosis
Department of Medicine, Harbor-UCLA Medical Center, Torrance, California 90509, USA.
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