Asymmetric PCR Primers for Mycobacterium tuberculosis Detection
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Solution Overview
Problem
Current methods for diagnosing Mycobacterium tuberculosis (MTB) are hindered by difficulties in specimen collection and preparation, high DNA homology with other Mycobacteria, unusual homology with human genomic DNA, and low replication rates, leading to challenges in sensitivity and specificity, particularly in HIV co-infection scenarios and drug-resistant strains.
Innovation Solution
Development of novel synthetic oligonucleotides targeting the conserved ponA gene of MTB, which are used in asymmetric PCR to create highly sensitive and specific primers and probes for accurate detection and quantification of MTB in clinical samples, avoiding cross-reactivity with other Mycobacteria and human DNA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard PCR methods are used for MTB detection, then the diagnosis can be performed, but the sensitivity and specificity are insufficient due to high DNA homology with other Mycobacteria and human genomic DNA
Solution Approach 1:
The patent extracts and targets specific unique sequences within the ponA gene of MTB that are evolutionarily distant from other Mycobacteria. By designing primers and probes that specifically bind to these unique regions, the method extracts only the MTB-specific signal while leaving out cross-reactive sequences from other Mycobacteria and human DNA, thereby improving detection precision and eliminating harmful cross-reactivity.
Solution Approach 2:
The patent applies local quality by designing primers and probes that target specific local regions (conserved segments) of the ponA gene. These local regions are selected because they provide improved assay sensitivity and specificity. The primers and probes are engineered to bind precisely to these localized unique sequences, ensuring that only MTB complex members are detected while avoiding cross-reactivity with other Mycobacteria.
2Productivity
If conventional PCR amplification is used, then DNA amplification is achieved, but the long incubation periods and low replication rates of MTB make the process impractical
Solution Approach 1:
The patent employs asymmetric PCR methodology as a preliminary action that creates single-stranded DNA products in advance. This preliminary amplification step produces primarily single-stranded DNA amplicons that can be directly determined in capture-probe based systems, eliminating the need for long incubation periods and subsequent culture steps. The method achieves rapid diagnosis by performing the amplification and detection in a streamlined sequence.
Solution Approach 2:
The patent replaces the traditional mechanical culture system with a molecular biology-based PCR system. Instead of relying on the slow mechanical replication of MTB bacteria in culture media, the method uses enzymatic amplification of MTB DNA through asymmetric PCR. This substitution of the detection mechanism from biological replication to molecular amplification dramatically reduces the time required for diagnosis.
3Measurement precision
If asymmetric PCR is used to produce single-stranded DNA products, then detection sensitivity is improved, but the amplification protocol complexity increases
Solution Approach 1:
The patent applies parameter changes by using asymmetric PCR with a 40:1 ratio of the two primers. This parameter change in primer concentration ratio produces primarily single-stranded DNA products instead of double-stranded products. The single-stranded amplicons are ideal for capture-probe based detection systems, significantly improving detection sensitivity. The parameter change is implemented through a well-defined protocol that manages the increased complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The approach achieves enhanced sensitivity and specificity, allowing for the detection of as low as 0.01 MTB genomes per PCR reaction, improving upon existing methods like Cepheid's GeneXpert MTB/RIF, with the ability to quantify MTB loads across a wide range and detect drug resistance markers.
Implementation Method 1
The primers and/or probes are useful for accurate quantification of MTB loads in clinical samples... Said methods utilize judiciously selected primers and probes that are capable of uniquely detecting MTB while avoiding other Mycobacteria, contaminating bacteria, and human DNA
Implementation Method 2
the asymmetric PCR methodology that produces primarily single stranded DNA products (that result from asymmetric PCR) amplify in a reproducible linear fashion
Data Source
AI summary
This invention pertains to probes, primers and associated methods suitable for the analysis and diagnosis of Myco-bacterium tuberculosis, among other things.