Investigating the Survival Response of Staphylococcus aureus to the Antimicrobial Lipid Sphingosine

Chen, Y (2018) Investigating the Survival Response of Staphylococcus aureus to the Antimicrobial Lipid Sphingosine. PhD thesis, University of Liverpool.

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Abstract

The human skin surface is covered with a lipid film that forms the interface between the viable epidermal layers and outer environment, and influences the colonisation of bacteria. Hydrolysis of the epidermal lipid ceramide via ceramidase yields sphingosine, an antimicrobial lipid that is able to kill staphylococci rapidly. Studies of patients with atopic dermatitis have indicated a correlation between levels of sphingosine and S. aureus colonisation of human skin, yet the contribution of sphingosine to the composition of the human skin microbiome and microbiota colonisation is unclear. This study investigates the effect of the host epidermal antimicrobial lipid D-sphingosine on S. aureus and S. epidermidis, with a focus on discovering components that contribute to survival of the former. The methods RNA-Seq and qPCR were used to dissect the transcriptional responses of S. aureus Newman and S. epidermidis Tü3298 after challenge with D-sphingosine. S. aureus displayed a large set of differentially expressed genes (1331), which contrasted with a smaller set for S. epidermidis (340). There was a clearly defined stimulon that was common between the species that included pathways for energy maintenance, amino acid and ion transport and metabolism, and protein repair. Previously reported transcriptomic responses to multiple cell wall and membrane-targeting antimicrobials shared commonalities with the response to sphingosine that supports its reported mode of action at the cell surface with membrane damage. The VraSR cell wall stress stimulon was upregulated in both species. Each species displayed pronounced upregulation of a putative phosphate-specific ABC transporter system encoded by the pstS-pstCAB operons. Experiments identified a contribution of this transport system to sphingosine survival and phosphate supplementation was shown to markedly increase sphingosine survival. Previous studies by the Horsburgh group identified experimentally evolved S. aureus strains with high levels of D-sphingosine resistance after serial passage with increasing concentrations of the lipid. SNPs associated with increased resistance were determined by genome resequencing and some of these were localised to the farER genes encoding a FarR-regulated FarE (mmpL) lipid efflux transporter. An isogenic farR SNP mutant of S. aureus was generated using molecular genetics approaches and showed a 10-fold higher MIC for D-sphingosine compared with the wild type Newman strain, indicating that the purported FarER fatty acid efflux system may have the capacity to mediate transport of sphingosine. The study findings of a link between sphingosine challenge and phosphate metabolism indicates future research potential to study host spingosine-1-phosphate in staphylococcal lifecycles, during health and disease.

Item Type:	Thesis (PhD)
Divisions:	Faculty of Health and Life Sciences > Faculty of Health and Life Sciences
Depositing User:	Symplectic Admin
Date Deposited:	21 Aug 2018 10:13
Last Modified:	19 Jan 2023 06:35
DOI:	10.17638/03020133
Supervisors:	Horsburgh, Malcom
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3020133