Direct comparison of Xpert MTB/RIF assay with liquid and solid mycobacterial culture for quantification of early bactericidal activity
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The early bactericidal activity of antituberculosis agents is usually determined by measuring the reduction of the sputum mycobacterial load over time on solid agar medium or in liquid culture. This study investigated the value of a quantitative PCR assay for early bactericidal activity determination. Groups of 15 patients were treated with 6 different antituberculosis agents or regimens. Patients collected sputum for 16 h overnight at baseline and at days 7 and 14 after treatment initiation. We determined the sputum bacterial load by CFU counting (log CFU/ml sputum, reported as mean ± standard deviation [SD]), time to culture positivity (TTP, in hours [mean ± SD]) in liquid culture, and Xpert MTB/RIF cycle thresholds (TC, n [mean ± SD]). The ability to discriminate treatment effects between groups was analyzed with one-way analysis of variance (ANOVA). All measurements showed a decrease in bacterial load from mean baseline (log CFU, 5.72 ± 1.00; TTP, 116.0 ± 47.6; TC, 19.3 ± 3.88) to day 7 (log CFU, −0.26 ± 1.23, P = 0.2112; TTP, 35.5 ± 59.3, P = 0.0002; TC, 0.55 ± 3.07, P = 0.6030) and day 14 (log CFU, −0.55 ± 1.24, P = 0.0006; TTP, 54.8 ± 86.8, P < 0.0001; TC, 2.06 ± 4.37, P = 0.0020). The best discrimination between group effects was found with TTP at day 7 and day 14 (F = 9.012, P < 0.0001, and F = 11.580, P < 0.0001), followed by log CFU (F = 4.135, P = 0.0024, and F = 7.277, P < 0.0001). TC was not significantly discriminative (F = 1.995, P = 0.091, and F = 1.203, P = 0.316, respectively). Culture-based methods are superior to PCR for the quantification of early antituberculosis treatment effects in sputum.
Kayigire , X A , Friedrich , S O , Venter , A , Dawson , R , Gillespie , S H , Boeree , M J , Heinrich , N , Hoelscher , M & Diacon , A H 2013 , ' Direct comparison of Xpert MTB/RIF assay with liquid and solid mycobacterial culture for quantification of early bactericidal activity ' Journal of Clinical Microbiology , vol 51 , no. 6 , pp. 1894-1898 . DOI: 10.1128/JCM.03290-12
Journal of Clinical Microbiology
Copyright © 2013, American Society for Microbiology. All Rights Reserved.
This study was conducted as an activity of the Pan African Consortium for the Evaluation of Anti-tuberculosis Antibiotics (PanACEA). PanACEA is funded by EDCTP grants CT.2004.32011.001, IP.2007.32011.011, IP.2007.32011.012, and IP.2007.32011.013, the Bill and Melinda Gates Foundation, the UK Medical Research Council, and the German Ministry of Science and Technology (BmBF; grant 01KA0901). A specific Ph.D. stipend was given by PanACEA to X. A. Kayigire to foster local career development.
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