Experimental evolution of Staphylococcus aureus in macrophages: dissection of a conditional adaptive trait promoting intracellular survival

Joana Alves, Manouk Vrieling, Natalie Ring, Gonzalo Yebra, Amy Pickering, Tomasz K Prajsnar, Stephen A. Renshaw, Ross Fitzgerald

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Staphylococcus aureus is a major pathogen associated with important diseases in humans and animals. Macrophages are a key component of the innate immune response to S. aureus infection and play a major role in disease outcome. In order to investigate the adaptive evolution of S. aureus in response to macrophages, we developed an experimental infection assay. S. aureus strains representing major human epidemic clones were passaged many times in a macrophage cell line, accumulating mutations in an array of genomic loci. Phenotypic analysis revealed the emergence of a lineage exhibiting increased survival in macrophages and human blood, and resistance to vancomycin. The evolved lineage exhibited a previously undescribed small colony variant (SCV) phenotype characterized by hyper-pigmentation, which resulted from a missense mutation in rsbW. Notably, the novel SCV was a conditional adaptive trait that was unstable in nutrient-replete conditions in vitro, rapidly converting from hyper-pigmented SCV to a non pigmented large colony variant via spontaneous sigB deletion events. Importantly, we identified similar deletions in the genome sequences of a limited number of clinical S. aureus isolates from public databases, indicating that related events may occur during clinical infection. Experimental infection of zebrafish did not reveal a difference in virulence between parent and novel SCV, but demonstrated an in vivo fitness cost for the compensatory sigB deletion events. Taken together, we report an experimental evolutionary approach for investigating bacterial innate immune cell interactions, revealing a conditional adaptation that promotes S. aureus survival in macrophages and resistance to vancomycin.
Original languageEnglish
Pages (from-to)1-19
Number of pages19
JournalmBio
Early online date29 Apr 2024
DOIs
Publication statusE-pub ahead of print - 29 Apr 2024

Keywords / Materials (for Non-textual outputs)

  • Staphylococcus aureus
  • antibiotic resistance
  • macrophages
  • evolution

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