Serial daptomycin selection generates daptomycin-nonsusceptible Staphylococcus aureus strains with a heterogeneous...

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Daptomycin is a crucial antibiotic for treating infections caused by Gram-positive bacteria, particularly methicillin-resistant Staphylococcus aureus (MRSA).
• Understanding the mechanisms of daptomycin resistance is essential for developing strategies to overcome treatment failures.

Purpose of the Study:

• To investigate the molecular mechanisms underlying daptomycin resistance in MRSA.
• To characterize the phenotypic and transcriptomic changes associated with acquired daptomycin nonsusceptibility.

Main Methods:

• Generation of daptomycin-nonsusceptible and revertant MRSA strains through in vitro selection and drug-free passaging.
• Analysis of membrane fluidity, membrane potential, and cell wall thickness using biophysical techniques and electron microscopy.
• Microarray analysis to compare gene expression profiles between resistant, revertant, and parental strains.

Main Results:

• The daptomycin-nonsusceptible strain exhibited increased membrane potential and a thicker cell wall compared to the parental strain.
• Downregulation of genes involved in teichoic acid synthesis (tagA, tagG) and cardiolipin synthesis (cls) was observed.
• Upregulation of the vraSR two-component regulatory system and ATP-binding cassette transporter genes (vraF, vraG) was noted in the resistant strain.
• Increased minimum inhibitory concentrations (MICs) for vancomycin and teicoplanin were observed in the resistant strain.

Conclusions:

• Daptomycin resistance in MRSA is associated with alterations in membrane potential, cell wall structure, and specific gene expression patterns.
• The observed transcriptional profile partially overlaps with that of heterogeneous vancomycin-intermediate S. aureus, suggesting potential cross-resistance mechanisms.
• The findings provide insights into the complex mechanisms of daptomycin resistance and potential therapeutic vulnerabilities.