Adaptations of Vancomycin-Intermediate Sequence Type 72 Methicillin-Resistant Staphylococcus aureus for Daptomycin...

Area of Science:

• Microbiology
• Infectious Diseases
• Molecular Biology

Background:

• Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is a significant pathogen, with ST72-MRSA-IV being the major clonal type in Korea.
• Vancomycin (VAN) intermediate resistance in MRSA is a growing concern, necessitating research into its underlying mechanisms.

Purpose of the Study:

• To investigate the role of specific genetic mutations in the cell envelope alterations and daptomycin (DAP) non-susceptibility of ST72-MRSA-IV.
• To assess the impact of these mutations on susceptibility to DAP and cationic antimicrobial peptides (CAMPs), cell envelope phenotypes, and host immune response.

Main Methods:

• Utilized isogenic pairs of vancomycin-susceptible (VSSA) and vancomycin-intermediate (VISA) ST72-MRSA-IV strains.
• Complemented VSSA strains with plasmids expressing single-point mutated genes identified in VISA strains.
• Assessed DAP and CAMP susceptibility, cell wall autolysis, surface charge, membrane potential (ΔΨ), gene expression, and cytokine stimulation in macrophages.

Main Results:

• The vraR_E127K mutation enhanced positive surface charge and thickened the cell wall via mprF- and dltABCD-independent mechanisms.
• No single-point mutated genes conferred increased DAP resistance.
• The DAP non-susceptible (DAP-NS) phenotype in the VISA strain resulted from combined low ΔΨ and increased positive surface charge.

Conclusions:

• Physicochemical alterations in the cell envelope, particularly increased positive surface charge and thickened cell wall, are implicated in the survival of DAP-NS VISA strains.
• The development of DAP non-susceptibility in MRSA is likely multifactorial, involving combined effects on membrane potential and cell surface properties.