DNA extraction from primary liquid blood cultures for bloodstream infection diagnosis using whole genome sequencing

J Med Microbiol. 2018 Mar;67(3):347-357. doi: 10.1099/jmm.0.000664. Epub 2018 Jan 10.

Abstract

Purpose: Speed of bloodstream infection diagnosis is vital to reduce morbidity and mortality. Whole genome sequencing (WGS) performed directly from liquid blood culture could provide single-assay species and antibiotic susceptibility prediction; however, high inhibitor and human cell/DNA concentrations limit pathogen recovery. We develop a method for the preparation of bacterial DNA for WGS-based diagnostics direct from liquid blood culture.

Methodology: We evaluate three commercial DNA extraction kits: BiOstic Bacteraemia, Amplex Hyplex and MolYsis Plus. Differential centrifugation, filtration, selective lysis and solid-phase reversible immobilization bead clean-up are tested to improve human cells/DNA and inhibitor removal. Using WGS (Illumina/MinION), we assess human DNA removal, pathogen recovery, and predict species and antibiotic susceptibility inpositive blood cultures of 44 Gram-negative and 54 Staphylococcus species.Results/Key findings. BiOstic kit extractions yield the greatest mean DNA concentration, 94-301 ng µl-1, versus 0-2.5 ng µl-1 using Amplex and MolYsis kits. However, we note higher levels of inhibition (260/280 ratio 0.9-2.1) and human DNA (0.0-4.4×106 copies) in BiOstic extracts. Differential centrifugation (2000 g, 1 min) prior to BiOstic extraction reduces human DNA by 63-89 % with selective lysis minimizing by a further 62 %. Post-extraction bead clean-up lowers inhibition. Overall, 67 % of sequenced samples (Illumina MiSeq) contain <10 % human DNA, with >93 % concordance between WGS-based species and susceptibility predictions and clinical diagnosis. If >60 % of sequencing reads are human (7/98 samples) susceptibility prediction becomes compromised. Novel MinION-based WGS (n=9) currently gives rapid species identification but not susceptibility prediction.

Conclusion: Our method for DNA preparation allows WGS-based diagnosis direct from blood culture bottles, providing species and antibiotic susceptibility prediction in a single assay.

Keywords: bacteraemia; bloodstream infection; sepsis; whole genome sequencing.

Publication types

  • Evaluation Study

MeSH terms

  • Bacteremia / diagnosis*
  • Bacteremia / microbiology
  • Blood Culture*
  • Catheter-Related Infections / diagnosis
  • Catheter-Related Infections / microbiology
  • DNA, Bacterial / analysis
  • DNA, Bacterial / genetics
  • DNA, Bacterial / isolation & purification*
  • Escherichia coli / genetics
  • Genome, Bacterial*
  • Humans
  • Microbial Sensitivity Tests
  • Molecular Diagnostic Techniques / methods
  • Reagent Kits, Diagnostic
  • Sequence Analysis, DNA / methods
  • Staphylococcus aureus / genetics
  • Whole Genome Sequencing*

Substances

  • DNA, Bacterial
  • Reagent Kits, Diagnostic