Drug Susceptibility Testing in Mycobacterium Tuberculosis

Drug susceptibility testing (DST) in Mycobacterium tuberculosis remains the cornerstone of effective tuberculosis control, guiding the choice of therapy and informing public health strategies to combat drug-resistant strains. Phenotypic DST approaches traditionally rely on culture of the bacilli in liquid or solid media to determine the minimal inhibitory concentration of first- and second-line drugs. Although culture-based methods are considered the reference standard, they are slow and require sophisticated laboratory infrastructure. In response, molecular diagnostics have emerged to detect common resistance-conferring mutations directly from patient specimens, reducing turnaround time from weeks to hours. Innovations in microfluidics, colourimetric assays and point-of-care nucleic acid amplification tests have extended DST capacity to low-resource settings, while the increasing application of whole-genome sequencing promises comprehensive resistance profiles and insights into transmission dynamics. Despite these advances, challenges persist in interpreting genotypic results for rare or novel mutations and in validating rapid tests against diverse clinical strains. Ongoing efforts aim to integrate phenotypic and genotypic data, to standardise protocols for digital imaging and colour-based readouts, and to deploy near-patient platforms that combine speed, affordability and biosafety. The global significance of improved DST is underscored by rising rates of multidrug-resistant and extensively drug-resistant tuberculosis, which threaten to reverse recent gains in disease control unless rapid, reliable and accessible testing becomes universal.

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Drug Susceptibility Testing in Mycobacterium Tuberculosis publication trend

The graph below shows the total number of articles in drug susceptibility testing in mycobacterium tuberculosis across all publications each year (not limited to Nature Index journals).

Technical terms

Phenotypic DST: Laboratory measurement of bacterial growth inhibition by antimicrobial agents, typically via culture in liquid or solid media to determine minimal inhibitory concentrations.

Genotypic DST: Molecular detection of genetic mutations in M. tuberculosis genes that confer drug resistance, often by PCR-based assays or sequencing.

Minimal Inhibitory Concentration (MIC): The lowest concentration of a drug that prevents visible growth of a microorganism under defined conditions.

Nucleic Acid Amplification Test (NAAT): A molecular technique, such as real-time PCR, that amplifies and detects specific DNA or RNA targets to identify pathogens or resistance mutations quickly.

Whole-Genome Sequencing (WGS): Comprehensive analysis of the entire bacterial genome to predict resistance profiles and inform epidemiological investigations.

Line Probe Assay: A strip-based molecular test that identifies specific resistance-associated mutations in gene regions of M. tuberculosis.

References

1. Establishing Compliance between Spectral, Colourimetric and Photometric Indicators in Resazurin Reduction Test. Bioengineering (2023).
2. The Effect of Inoculum Size on Antimicrobial Susceptibility Testing of Mycobacterium tuberculosis. Microbiology Spectrum (2023).
3. Diagnostic Accuracy of the Truenat MTB Plus Assay and Comparison with the Xpert MTB/RIF Assay to Detect Tuberculosis among Hospital Outpatients in Cameroon. Journal of Clinical Microbiology (2022).
4. Tuberculosis Phenotypic and Genotypic Drug Susceptibility Testing and Immunodiagnostics: A Review. Frontiers in Immunology (2022).