Normally functioning murF is essential for the optimal expression of methicillin resistance in Staphylococcus aureus

Area of Science:

• Microbiology
• Molecular Biology
• Antibiotic Resistance

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant public health threat due to its resistance to beta-lactam antibiotics.
• Understanding the genetic and molecular mechanisms underlying MRSA resistance is crucial for developing effective treatment strategies.

Purpose of the Study:

• To investigate the role of the murF gene in the antibiotic resistance of MRSA.
• To characterize the impact of murF disruption on cell wall synthesis and beta-lactam resistance in MRSA strain COL.

Main Methods:

• Construction and integration of a suicide plasmid into the chromosomal copy of the murF gene in MRSA strain COL using Campbell type integration.
• Determination of oxacillin minimum inhibitory concentration (MIC) values for the parental and mutant strains.
• Analysis of peptidoglycan composition and cell wall precursors in the mutant.
• Northern analysis to assess mecA gene transcription.

Main Results:

• Disruption of murF in MRSA strain COL resulted in a significant decrease in oxacillin resistance (MIC reduced from 400 µg/ml to 0.75 µg/ml) in 90% of the cells.
• The murF mutation selectively affected beta-lactam antibiotic resistance, with no change in susceptibility to other antibiotics like vancomycin.
• Analysis revealed alterations in peptidoglycan structure, including abnormal muropeptide components and accumulation of UDP-MurNAc-tripeptide, indicating impaired cell wall synthesis.
• Heterogeneous subpopulations within the mutant cultures retained high-level oxacillin resistance, exhibiting normal peptidoglycan structure and increased mecA transcription.

Conclusions:

• The murF gene plays a critical role in maintaining high-level beta-lactam resistance in MRSA.
• MRSA resistance mechanisms are complex, involving subpopulations with distinct genetic and biochemical profiles.
• Targeting murF or related cell wall synthesis pathways could be a potential strategy for combating MRSA infections, but resistance evolution needs consideration.