Broad-Range 16S PCR
Related: PCR · Sanger Sequencing · 16S Amplicon Analysis · Carl Woese · Culture and Isolation
1. Principle
Universal (or broad-range) primers amplify conserved regions of bacterial 16S rRNA genes from clinical material; sequencing the amplicon identifies bacteria when culture is negative or slow — especially in normally sterile sites.
2. Step-by-Step Procedure (conceptual)
- Strict contamination control (reagents can contain bacterial DNA).
- Extract DNA from CSF, tissue, valve, etc. (DNA Extraction).
- Amplify 16S (full or partial V regions).
- Sanger Sequencing (single dominant organism) or NGS amplicon read (16S Amplicon Analysis) for mixtures.
- BLAST / curated DB identification; correlate with Gram stain and clinic.
3. Interpretation
- Powerful for monomicrobial sterile-site infections (e.g., culture-negative endocarditis, meningitis).
- Pitfalls: Contaminating skin flora DNA; polymicrobial samples hard by Sanger; resolution may stop at genus; dead bacteria still amplify.
4. Clinical Use Cases
- Culture-negative endocarditis / device infections.
- Brain abscess, septic arthritis after antibiotics.
- Complement, not replace, culture/AST when organism grows.
5. Comparison with Other Methods
| Method | Best for |
|---|---|
| Broad-range 16S | Unknown bacteria, sterile site, prior antibiotics |
| Targeted Multiplex PCR | Known syndrome menu |
| Metagenomic NGS | Bacteria + viruses + fungi (broader) |
| Culture | Viable organism + AST |
6. Mnemonic / Visual Aid
When culture is silent, 16S can still speak — carefully.
Active Recall
- Why are reagent blanks critical?
- Why is Sanger poor for polymicrobial abscesses?
- Does 16S provide AST results?