Impact of psm-mec in Methicillin-Resistant Staphylococcus aureus (ST764) Strains Isolated from Keratitis Patients

Area of Science:

• Ophthalmology
• Microbiology
• Genetics

Background:

• Staphylococcus aureus is a major cause of keratitis.
• Methicillin-resistant S. aureus (MRSA) is an increasing concern in bacterial keratitis.
• Previous work identified ST5 and ST764 as key MRSA lineages in keratitis.

Purpose of the Study:

• To investigate and compare the virulence properties of MRSA keratitis isolates from ST5 and ST764 lineages.
• To identify specific virulence determinants contributing to observed differences.

Main Methods:

• Multi-locus sequence typing to classify MRSA isolates.
• Analysis of virulence gene prevalence (adhesions, toxins).
• Assessment of biofilm formation, colony spreading, hemolytic activity, and alpha-phenol-soluble modulin production.
• Evaluation of isolate supernatant toxicity on corneal epithelial cells.

Main Results:

• No significant difference in the prevalence of common virulence genes between ST5 and ST764 isolates.
• ST5 isolates possessed an intact psm-mec gene, promoting biofilm formation.
• ST764 isolates had a point mutation in psm-mec, correlating with higher colony spreading, hemolytic activity, and alpha-phenol-soluble modulin production.
• ST5 isolates exhibited significantly higher biofilm production compared to ST764 isolates.
• ST764 isolate supernatants demonstrated greater toxicity to corneal epithelial cells than ST5 supernatants.

Conclusions:

• A point mutation in the psm-mec gene in ST764 MRSA isolates is associated with distinct virulence characteristics compared to ST5 isolates.
• This mutation contributes to increased corneal epithelial cell toxicity and altered pathogenic behavior in MRSA keratitis.
• Understanding these genotypic and phenotypic differences is crucial for managing MRSA keratitis.