Nested qPCR Assay for Tuberculosis Detection

The patent employs a nested qPCR assay where external primers first amplify a larger target region, followed by internal primers that amplify a smaller nested region within the first amplicon. This nested approach enhances detection sensitivity by enriching the target sequence through sequential amplification, while maintaining a relatively simple procedural framework that builds upon conventional PCR methodology.

The detection method is divided into two distinct segmentation stages: (1) a screening phase using conventional qPCR to identify potential positives, and (2) a confirmation phase using nested qPCR to verify results with higher sensitivity. This segmentation allows the system to balance speed and simplicity in the first stage with high sensitivity in the second stage, effectively resolving the contradiction between procedural simplicity and detection sensitivity.

The patent replaces the conventional mechanical/cultural method of TB diagnosis (which requires 3-8 weeks of culture time) with a molecular biology-based qPCR method. This substitution utilizes enzymatic amplification of DNA sequences rather than bacterial cultivation, dramatically reducing the diagnostic time from weeks to hours while maintaining or improving both sensitivity and specificity through targeted nucleic acid detection.

The nested qPCR assay performs preliminary enrichment of the target DNA sequence through the first round of amplification with external primers, creating a concentrated template for the second round of amplification. This preliminary action ensures that even low-abundance TB DNA in paucibacillary specimens is sufficiently amplified to achieve high sensitivity detection, while the entire process completes in hours rather than weeks.

The nested qPCR design uses external primers to amplify a larger initial region, followed by internal primers that amplify a smaller nested region within the first amplicon. This nested approach provides two layers of specificity: the external primers capture the target broadly, while the internal primers provide a second layer of discrimination that reduces cross-reactivity with non-tuberculosis mycobacteria, thereby improving both sensitivity and specificity while maintaining rapid detection.

The patent optimizes multiple parameters including annealing temperatures for external and internal primers, primer concentrations, and cycling conditions to enhance amplification efficiency and specificity. By carefully adjusting these parameters, the method achieves high sensitivity for paucibacillary specimens while minimizing false positives through conditions that favor specific TB DNA amplification over cross-reactive amplification.