Highly sensitive sequence specific qPCR detection of Mycobacterium tuberculosis complex in respiratory specimens

Area of Science:

• Molecular biology
• Microbiology
• Medical diagnostics

Background:

• Nucleic acid amplification tests (NAATs) for Mycobacterium tuberculosis (MTB) exhibit reduced sensitivity in smear-negative sputum specimens, hindering tuberculosis diagnosis.
• PCR inhibitors, such as human genomic DNA, co-extracted during sample processing, can decrease NAAT sensitivity.
• A diagnostic gap exists for sensitive MTB detection in smear-negative samples.

Purpose of the Study:

• To design and validate a novel MTB screening assay with optimized sample preparation and quantitative PCR (qPCR) methods.
• To specifically address the lower sensitivity of current NAATs in smear-negative/culture-positive tuberculosis cases.
• To overcome the challenge of PCR inhibitors in sputum samples.

Main Methods:

• Developed a streamlined sample preparation method using detergent and proteolysis to reduce sputum viscosity and isolate MTB DNA.
• Designed a multiplexed qPCR assay targeting two MTB-specific loci (IS6110 and senX3-regX3) and a process control (Bacillus atrophaeus cotJC gene).
• Identified and addressed human genomic DNA as a significant qPCR inhibitor.

Main Results:

• The assay demonstrated a limit of detection of 20 cfu/ml, surpassing the Xpert® MTB/RIF assay.
• In a preliminary study of 60 sputum samples, the assay achieved 96% sensitivity and 100% specificity compared to the Xpert® MTB/RIF assay.
• The novel sample preparation effectively mitigated PCR inhibition.

Conclusions:

• The developed MTB screening assay shows high sensitivity and specificity, particularly for smear-negative samples.
• This assay offers a promising solution to improve tuberculosis diagnosis by overcoming limitations of existing NAATs.
• The optimized sample preparation and multiplexed qPCR provide a robust method for MTB detection.