Contaminant and Mixed-Culture Detection
One-Sentence Definition
Contaminant and mixed-culture detection identifies when sequencing reads or assemblies contain more than one organism — or lab reagents/human DNA — so downstream typing and AMR calls are not trusted blindly.
Simple Explanation
Make sure the genome you’re analyzing is one bacterium, not a soup of two bugs plus kit DNA.
Detailed Scientific Explanation
| Signal | Suspicious for |
|---|---|
| Multiple 16S / GTDB hits | Mixed culture |
| CheckM high contamination | Strain heterogeneity or mix |
| Conflicting MLST alleles | Mix or recombination artifact |
| Unexpected AMR from wrong taxon | Contaminant gene |
| High human/index reads | Host contamination |
Tools: Kraken2/Centrifuge read classifiers, ConFindr, CheckM, MIDAS-style approaches, manual coverage plots.
Especially critical for metagenomic diagnostics and primary culture plates that are impure.
Mechanism
Classify reads/contigs taxonomically → quantify major vs minor taxa → apply pass/fail rules before WGS Bioinformatics Pipeline reporting.
Clinical Importance
- Prevents false MDR calls and false outbreak links.
- Guides re-culture vs cautious interpretation.
Research Importance
- Data integrity for public genome repositories.
Diagnostic Relevance
- Mandatory QC node in accredited WGS workflows (Assembly Quality Control).
AMR Relevance
High risk of false positives if contaminant DNA carries resistance genes.
Related Methods
Related MOCs
Active Recall Questions
- Name two computational red flags for mixed cultures.
- Why is AMR calling dangerous on contaminated assemblies?
- When should you resequence vs bioinformatically filter?