Staphylococcus aureus Cell Wall Biosynthesis Modulates Bone Invasion and Osteomyelitis Pathogenesis

Area of Science:

• Microbiology
• Infectious Diseases
• Biomedical Engineering

Background:

• Staphylococcus aureus chronic osteomyelitis involves bacterial invasion of the osteocyte lacuno-canalicular network (OLCN).
• Penicillin binding protein 4 (PBP4) and S. aureus surface protein C (SasC) were previously implicated in bacterial deformation and nanopore passage.

Purpose of the Study:

• To investigate the roles of S. aureus cell wall synthesis machinery and surface adhesins in OLCN invasion and osteomyelitis pathogenesis.
• To test the hypothesis that cell wall synthesis enables durotaxis and surface adhesins enable haptotaxis for OLCN invasion.

Main Methods:

• In vitro nanopore propagation assays using a microfluidic silicon membrane-canalicular array (μSiM-CA).
• In vivo murine model for implant-associated osteomyelitis.
• Transmission electron microscopy (TEM) for imaging bacterial invasion in bone.

Main Results:

• Deletion of pbp3, atl, clfA, and sasC reduced S. aureus nanopore propagation in vitro.
• In vivo, cell wall synthesis mutants (Δpbp3, Δatl) significantly reduced implant loosening and abscess formation.
• Δpbp3 also decreased peri-implant osteolysis, osteoclast activity, and RANKL production, with TEM confirming reduced in vivo canalicular invasion.

Conclusions:

• S. aureus cell wall synthesis enzymes, especially PBP3, are critical for invasion of the OLCN and osteomyelitis pathogenesis.
• Surface adhesins play a minimal role in osteomyelitis progression compared to cell wall synthesis machinery.
• Targeting S. aureus cell wall synthesis pathways may offer a therapeutic strategy for chronic osteomyelitis.