Comparison of quantitative techniques including Xpert MTB/RIF to evaluate mycobacterial burden
Date
2011-12
Journal Title
Journal ISSN
Volume Title
Publisher
PLOS
Abstract
Introduction: Accurate quantification of mycobacterial load is important for the evaluation of patient infectiousness,
disease severity and monitoring treatment response in human and in-vitro laboratory models of disease. We hypothesized
that newer techniques would perform as well as solid media culture to quantify mycobacterial burden in laboratory
specimens.
Methods: We compared the turn-around-time, detection-threshold, dynamic range, reproducibility, relative discriminative
ability, of 4 mycobacterial load determination techniques: automated liquid culture (BACTEC-MGIT-960), [3H]-uracil
incorporation assays, luciferase-reporter construct bioluminescence, and quantitative PCR(Xpert -MTB/RIF) using serial
dilutions of Mycobacterium bovis and Mycobacterium tuberculosis H37RV. Mycobacterial colony-forming-units(CFU) using
7H10-Middlebrook solid media served as the reference standard.
Results: All 4 assays correlated well with the reference standard, however, bioluminescence and uracil assays had a
detection threshold $16103 organisms. By contrast, BACTEC-MGIT-960 liquid culture, although only providing results in
days, was user-friendly, had the lowest detection threshold (,10 organisms), the greatest discriminative ability (1 vs. 10
organisms; p = 0.02), and the best reproducibility (coefficient of variance of 2% vs. 38% compared to uracil incorporation;
p = 0.02). Xpert-MTB/RIF correlated well with mycobacterial load, had a rapid turn-around-time (,2 hours), was user
friendly, but had a detection limit of ,100 organisms.
Conclusions: Choosing a technique to quantify mycobacterial burden for laboratory or clinical research depends on
availability of resources and the question being addressed. Automated liquid culture has good discriminative ability and low
detection threshold but results are only obtained in days. Xpert MTB/RIF provides rapid quantification of mycobacterial
burden, but has a poorer discrimination and detection threshold.
Description
The original publication is available at www.plosone.org
Keywords
Mycobacterial load, Patient infectiousness, Mycobacterium tuberculosis
Citation
Van Zyl-Smit, R. N. et al. 2011. Comparison of Quantitative Techniques including Xpert MTB/RIF to Evaluate Mycobacterial Burden. PLoS ONE, 6(12): e28815, doi:10.1371/journal.pone.0028815.