Targeted Next Generation Sequencing (tNGS)

Targeted Next-Generation Sequencing (tNGS): tNGS is an advanced molecular diagnostic technique that focuses on sequencing specific regions of the Mycobacterium tuberculosis (MTB) genome known to be associated with drug resistance. Unlike traditional culture-based drug susceptibility testing (DST), which can take weeks to deliver results, tNGS can rapidly identify genetic mutations linked to resistance within days, significantly improving the speed and accuracy of TB diagnosis.

Steps involved in the process of tNGS:

1. Sample collection: A patient’s sputum or other sample is collected.
2. DNA extraction: The DNA of the TB bacteria is isolated from the sample.
3. Target selection: Only certain regions of the DNA that are linked to drug resistance are chosen for sequencing.
4. Sequencing: The selected DNA regions are read using next-generation sequencing machines, which can process many samples at once.
5. Data analysis: Specialized software identifies mutations in the DNA that indicate resistance to TB drugs.

This method does not always require growing the bacteria in the lab, which saves a lot of time compared to culture-based methods.

Impact on TB Diagnosis:

1. Rapid and comprehensive DR profiling: It can provide results within a few days, compared to weeks for traditional testing. By targeting multiple resistance-associated genes, tNGS enables simultaneous detection of mutations conferring resistance to first- and second-line anti-TB drugs.
2. More Sensitive: It can detect mixed infections and low-frequency resistance mutations that may be missed by phenotypic or PCR-based tests.
3. Better patient care: Clinicians can quickly choose the most effective drugs for treatment, reducing treatment failure and improving recovery.
4. Differentiation Between TB & NTM Infections: Prevents misdiagnosis of TB in cases where NTM is present.
5. Scalability and cost-effectiveness: Since it sequences only selected genomic regions, tNGS is more affordable and easier to implement in resource-limited settings than WGS.
6. Public health benefit: Rapid detection helps prevent the spread of drug-resistant TB in communities.

Scope and Applications

1. Testing for multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB.
2. Supporting research to understand how TB bacteria evolve and spread.
3. Helping public health laboratories monitor patterns of drug resistance in populations.
4. Because tNGS focuses only on specific genes, it is faster and less expensive than whole-genome sequencing, making it more practical for use in hospitals and national TB programs, even in low- and middle-income countries.

Future of tNGS in TB Diagnostics

The future of tNGS looks promising. As technology becomes cheaper and easier to use, more countries will be able to include it in their TB testing systems. Integration with other molecular tools and artificial intelligence could make data analysis even faster and more accurate. Eventually, tNGS could become a routine test for TB diagnosis and drug-resistance monitoring worldwide.