Distinct Vasculotropic vs. Osteotropic Features of S. agalactiae vs. S. aureus Implant-Associated Bone Infection in Mice

Osteomyelitisis a devastating complication of orthopaedic surgeryand commonly caused by Staphylococcus aureus ( S. aureus) andGroup B Streptococcus (GBS, S. agalactiae ). Clinically, S. aureus osteomyelitis is associated with local inflammation, abscesses, aggressive osteolysis, and septic implant loosening. In contrast, S. agalactiae orthopaedic infections generally involve soft tissue, with acute life-threatening vascular spread. While pre-clinical models that recapitulate the clinical features of S. aureus bone infectionhave proven useful for research, no animal models of S. agalactiae osteomyelitisexist.Here, we compared the pathology caused by these bacteria in an established murine model of implant-associated osteomyelitis. In vitroscanning electron microscopy and CFU quantification confirmed similar implant inocula for both pathogens (~10 5 CFU/pin). Assessment of mice at 14 dayspost-infection demonstrated increased S. aureus virulence, since S. agalactiae infected mice had significantly greater body weight, and fewer CFU on the implant, bone and adjacent soft tissue (p