Alternative mutational pathways to intermediate resistance to vancomycin in methicillin-resistant Staphylococcus...

Area of Science:

• Microbiology
• Genetics
• Infectious Diseases

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat in healthcare settings.
• The emergence of vancomycin-intermediate S. aureus (VISA) complicates treatment options.
• Understanding the genetic basis of VISA is crucial for developing effective therapies.

Purpose of the Study:

• To compare phenotypic and genotypic changes during the selection of MRSA mutants with low-level vancomycin resistance.
• To investigate the genetic pathways leading to vancomycin-intermediate resistance in MRSA.

Main Methods:

• Utilized two in vitro experimental systems: a pharmacokinetic/pharmacodynamic (PK/PD) model of simulated endocardial vegetations (SEVs) and exposure to vancomycin in laboratory growth medium.
• Selected vancomycin-resistant mutants from MRSA strain JH1.
• Compared phenotypic abnormalities and sequenced whole genomes of selected mutants.

Main Results:

• Two mutants, JH1R1 (from PK/PD model) and JH1R2 (from growth medium), exhibited reduced vancomycin and daptomycin susceptibility.
• Both mutants showed phenotypic alterations characteristic of in vivo VISA.
• Genome sequencing revealed distinct mutations in JH1R1 (including in yycG) and JH1R2 (including in rpoB).

Conclusions:

• MRSA strain JH1 can acquire VISA-type resistance via multiple distinct genetic routes.
• The identified mutations provide insight into the mechanisms of vancomycin resistance development in MRSA.