Metagenomic NGS
Related: Metagenomics · NGS Library Preparation · DNA Extraction · RNA Extraction · Broad-Range 16S PCR · Contaminant and Mixed-Culture Detection
1. Principle
Metagenomic next-generation sequencing (mNGS) sequences total DNA and/or RNA from a clinical specimen without predefining the pathogen, then uses bioinformatics to detect and (sometimes) type microbes among abundant host nucleic acid.
2. Step-by-Step Procedure (conceptual)
- Collect sterile-site or prioritized specimens (Sample Types and Specimen Quality).
- Extract total NA; optional host depletion / microbial enrichment.
- Prepare DNA and/or RNA libraries (NGS Library Preparation).
- Sequence to sufficient depth.
- Bioinfo: remove host reads → classify microbial reads → apply thresholds → interpret with clinical ID specialist.
- Confirm critical findings with orthogonal PCR/culture when possible.
3. Interpretation
- Strength: Finds unexpected / unculturable / co-infections.
- Pitfalls: Contaminant databases; reagent flora; colonization; incomplete resistance phenotype; cost; turnaround.
- Reporting needs careful disclaimers — not a replacement for AST.
4. Clinical Use Cases
- Culture-negative meningitis/encephalitis, puzzling pneumonia, fever of unknown origin (select centers).
- Outbreak mystery pathogens.
- Complements Whole-Genome Sequencing of isolates when culture succeeds.
5. Comparison with Other Methods
| Method | Blind to novel pathogens? | AST |
|---|---|---|
| mNGS | Least blind | No (usually) |
| Multiplex PCR | Yes (off-panel) | Limited markers |
| Broad-Range 16S PCR | Bacteria-focused | No |
| Culture | Misses non-culturables | Yes |
6. Mnemonic / Visual Aid
Sequence first, ask questions later — then filter ruthlessly.
Related Concepts
- MOC - Bioinformatics in Microbiology · AI Diagnostics in Microbiology · FAIR Data and Genomic Surveillance
Active Recall
- Why is host depletion used?
- Name two false-positive sources in mNGS.
- Can mNGS alone guide antibiotic MIC selection?