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New TB Assay Identifies Bacteria and Drug-Resistance Markers

March 16th, 2017 / Christine Valle

March is TB Awareness Month

For Tuberculosis (TB) Awareness Month, we’re highlighting a paper from a team of scientists in China who developed a molecular test for tuberculosis.

Published in the Journal of Clinical Pathology, “Development and in-use evaluation of a novel Luminex MicroPlex microsphere-based (TRIOL) assay for simultaneous identification of Mycobacterium tuberculosis and detection of first-line and second-line antituberculous drug resistance in China,” comes from lead author Feifei Yin, senior author Kwok-Yung Yuen, and collaborators at Hainan Medical University and the University of Hong Kong.

New TB Assay Identifies Bacteria and Drug-Resistance Markers

While TB is a global health threat, it is especially prevalent in China, which accounts for 10% of all cases worldwide. “The lack of accessibility to healthcare facilities, coinfection with HIV, and poor compliance to drug treatment in rural parts of the country are important factors associated with this large disease burden and the high proportion of multidrug-resistant tuberculosis in China,” the authors report.

To combat the problem, there’s a need for rapid diagnostics that can provide highly accurate and reliable results. Conventional testing methods “are laborious and have long turnaround time,” the scientists note. Molecular tests have been gaining ground, but there is still room for improvement.

xMAP® Technology-based Assay Developed

For this study, the scientists developed their multiplexed assay using the Luminex xMAP® system. The assay tested not only for M. tuberculosis but also for common markers of drug resistance. (The team named it, in part, after some of these drugs, calling it TRIOL for Tuberculosis-Rifampicin-isoniazid-Ofloxacin-Luminex.) They evaluated the test by comparing its results to a polymerase chain reaction (PCR)-sequencing assay with phenotypic drug susceptibility testing.

The project involved testing 145 M. tuberculosis isolates as well as 12 non-TB samples. The TRIOL assay had 100% specificity and sensitivity, identifying TB in all 145 case samples and in none of the 12 controls. There were 87 samples without drug resistance, and results for these were concordant across the multiplex TRIOL assay and the PCR assay. The TRIOL test missed some isolates that were drug-resistant, but the authors noted that those samples had markers that were absent from their assay. “Importantly, the TRIOL assay did not miss any mutations that were included in the assay,” the scientists report, adding that future versions of this assay could be developed to include more resistance markers.

TRIOL Could Help Control Spread of TB in China

“Compared with our previously developed PCR-sequencing assays, the TRIOL assay has higher throughput, lower cost, and is less labor intensive,” the authors write. The assay detects far more types of resistance to anti-TB drugs than commonly used molecular tests and can run up to 96 samples at a time, generating results for large groups of people much faster than alternatives. “The TRIOL assay is particularly advantageous for use in regions with high prevalence of multidrug-resistant tuberculosis, such as China, because it has an open-architecture system which allows the addition of more specific primers to detect mutations that are rarely found elsewhere,” Yin et. al. write. They recommend additional testing of this assay on other types of clinical samples and express the hope that adoption of the TRIOL assay in other labs could help control the spread of drug-resistant TB in China.

Interested in learning more about novel xMAP assays to help identify and characterize tuberculosis? Read this blog:

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