Genomic exploration of sequential clinical isolates reveals a distinctive molecular signature of persistent Staphylococcus aureusbacteraemia

Stefano G. Giulieri, Sarah L. Baines, Romain Guerillot, Torsten Seemann, Anders Gonçalves da Silva, Mark Schultz, Ruth C. Massey, Natasha E. Holmes, Timothy P. Stinear, Benjamin P. Howden*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

11 Citations (Scopus)
256 Downloads (Pure)

Abstract

Background
Large-scale genomic studies of within-host diversity in Staphylococcus aureus bacteraemia (SAB) are needed to understanding bacterial adaptation underlying persistence and thus refining the role of genomics in management of SAB. However, available comparative genomic studies of sequential SAB isolates have tended to focus on selected cases of unusually prolonged bacteraemia, where secondary antimicrobial resistance has developed.

Methods
To understand the bacterial genetic diversity during SAB more broadly, we applied whole genome sequencing to a large collection of sequential isolates obtained from patients with persistent or relapsing bacteraemia. After excluding genetically unrelated isolates, we performed an in-depth genomic analysis of point mutations and chromosome structural variants arising within individual SAB episodes.

Results
We show that, while adaptation pathways are heterogenous and episode-specific, isolates from persistent bacteraemia have a distinctive molecular signature, characterised by a low mutation frequency and high proportion of non-silent mutations. Analysis of structural genomic variants revealed that these often overlooked genetic events are commonly acquired during SAB. We discovered that IS256 insertion may represent the most effective driver of within-host microevolution in selected lineages, with up to three new insertion events per isolate even in the absence of other mutations. Genetic mechanisms resulting in significant phenotypic changes, such as increases in vancomycin resistance, development of small colony phenotypes, and decreases in cytotoxicity, included mutations in key genes (rpoB, stp, agrA) and an IS256 insertion upstream of the walKR operon.

Conclusions
This study provides for the first time a large-scale analysis of within-host genomic changes during invasive S. aureus infection and describes specific patterns of adaptation that will be informative for both understanding S. aureus pathoadaptation and utilising genomics for management of complicated S. aureus infections.
Original languageEnglish
Article number65
Number of pages17
JournalGenome Medicine
Volume10
DOIs
Publication statusPublished - 23 Aug 2018

Keywords

  • Staphylococcus aureus
  • bacteraemia
  • genomics
  • within-host diversity
  • persistence

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