Causal role of single nucleotide polymorphisms within the mprF gene of Staphylococcus aureus in daptomycin resistance

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Single nucleotide polymorphisms (SNPs) in the mprF open reading frame (ORF) are frequently found in daptomycin-resistant (DAP(r)) Staphylococcus aureus.
• These SNPs are often linked to increased lysyl-phosphatidylglycerol (L-PG) synthesis or translocation, but their causal role in DAP(r) is uncertain.

Purpose of the Study:

• To determine if specific mprF SNPs are causal for daptomycin resistance in Staphylococcus aureus.
• To investigate the mechanism by which mprF SNPs contribute to DAP(r) phenotype.

Main Methods:

• Utilized an isogenic set of S. aureus strains, including wild-type, a ΔmprF mutant, and strains complemented with wild-type or mutated mprF ORFs.
• Cloned mprF ORFs with specific point mutations (mprFS295L, mprFT345A) from isogenic DAP-susceptible (DAP(s))-DAP(r) strain pairs.
• Assessed changes in daptomycin minimum inhibitory concentration (MIC), surface charge, and cell membrane phospholipid profiles.

Main Results:

• Complementation with singly point-mutated mprF genes (mprFS295L or mprFT345A) successfully recapitulated DAP(r) phenotypes observed in the original strains.
• Individual mprF SNPs were shown to alter DAP MICs, surface charge, and phospholipid profiles.
• Gain-in-function SNPs leading to enhanced L-PG synthesis were identified as likely drivers of reduced daptomycin binding via charge repulsion.

Conclusions:

• Specific point mutations within the mprF ORF are causally related to daptomycin resistance in the studied Staphylococcus aureus strains.
• Enhanced L-PG synthesis, driven by mprF gain-in-function SNPs, reduces daptomycin binding to the bacterial cell surface.
• mprF SNPs serve as a direct cause, not merely a biomarker, for daptomycin resistance in these strains.