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Free Content Xpert® MTB/RIF detection of Mycobacterium tuberculosis from sputum collected in molecular transport medium

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BACKGROUND: The Xpert® MTB/RIF assay is widely used for Mycobacterium tuberculosis detection. However, specimen transport remains a challenge. PrimeStore Molecular Transport Medium® (PS-MTM) inactivates specimens and stabilizes DNA/RNA at ambient temperature for subsequent molecular detection.

OBJECTIVE: To compare the detection of M. tuberculosis concentrations in PS-MTM using Xpert and real-time polymerase chain reaction (RT-PCR), and smear-positive sputum specimens collected using a flocked swab.

METHODS: Dilutions of M. tuberculosis in PS-MTM and phosphate buffered saline (PBS) were analyzed using the Xpert assay and commercial RT-PCR. Smear-positive (1+ to 3+) sputum specimens (n = 17) were transferred by flocked swab into PS-MTM and PBS, and were compared to standard 1.0 ml sputum Xpert analysis.

RESULTS: Using the Xpert assay, cycle threshold values from high M. tuberculosis concentrations in PS-MTM (>103 colony forming units [cfu]/ml) were increased compared to control. In contrast, M. tuberculosis samples containing <103 cfu/ml, i.e., low concentrations, suspended in PS-MTM resulted in detection down to 10 cfu/ml. Xpert detection efficiency in PS-MTM treated samples (63.2%) was improved compared to PBS controls (34.9%). Xpert detected M. tuberculosis in all sputum specimens collected by flocked swabs in PS-MTM, and correlated with routine Xpert detection.

CONCLUSIONS: PS-MTM enhances M. tuberculosis detection at low concentrations of M. tuberculosis, and provides a simplified and efficient collection method for Xpert detection.
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Keywords: PrimeStore MTM; Xpert; molecular transport medium; tuberculosis testing

Document Type: Research Article

Affiliations: 1: Longhorn Vaccines and Diagnostics, San Antonio, Texas, USA 2: University of Pretoria, Pretoria, South Africa 3: University of Pretoria, Pretoria, Anova Health Institute, Johannesburg, South Africa 4: City of Milwaukee Health Department Laboratory, Milwaukee, Wisconsin, USA 5: University of Texas at San Antonio, San Antonio, Texas, USA

Publication date: August 1, 2016

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  • The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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