Related Experiment Video
Updated: Nov 25, 2025
Animal Model of Implant-Associated Infections in Mice
Published on: June 27, 2025
Distinct vasculotropic versus osteotropic features of S. agalactiae versus S. aureus implant-associated bone
Elysia A Masters1,2, Stephanie P Hao1, H Mark Kenney1,3
1Center for Musculoskeletal Research, University of Rochester Medical Center, Rochester, New York, USA.
Abstract:
Osteomyelitis is a devastating complication of orthopaedic surgery and commonly caused by Staphylococcus aureus (S. aureus) and Group 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 preclinical models that recapitulate the clinical features of S. aureus bone infection have proven useful for research, no animal models of S. agalactiae osteomyelitis exist. Here, we compared the pathology caused by these bacteria in an established murine model of implant-associated osteomyelitis. In vitro scanning electron microscopy and CFU quantification confirmed similar implant inocula for both pathogens (~105 CFU/pin). Assessment of mice at 14 days post-infection demonstrated increased S. aureus virulence, as S. agalactiae infected mice had significantly greater body weight, and fewer CFU on the implant and in bone and adjacent soft tissue (p < 0.05). X-ray, µCT, and histologic analyses showed that S. agalactiae induced significantly less osteolysis and implant loosening, and fewer large TRAP+ osteoclasts than S. aureus without inducing intraosseous abscess formation. Most notably, transmission electron microscopy revealed that although both bacteria are capable of digesting cortical bone, S. agalactiae have a predilection for colonizing blood vessels embedded within cortical bone while S. aureus primarily colonizes the osteocyte lacuno-canalicular network. This study establishes the first quantitative animal model of S. agalactiae osteomyelitis, and demonstrates a vasculotropic mode of S. agalactiae infection, in contrast to the osteotropic behavior of S. aureus osteomyelitis.
Insights
This study developed the first animal model for Group B Streptococcus (GBS) osteomyelitis, revealing its distinct vasculotropic infection pattern compared to Staphylococcus aureus bone infections.
Area of Science:
- Orthopaedic Surgery
- Infectious Diseases
- Microbiology
Background:
- Osteomyelitis is a severe complication of orthopaedic surgery, often caused by Staphylococcus aureus (S. aureus) or Group B Streptococcus (GBS, S. agalactiae).
- S. aureus infections typically cause local bone destruction and implant loosening, while GBS infections often lead to systemic spread.
- Existing animal models effectively study S. aureus osteomyelitis, but models for GBS osteomyelitis are lacking.
Purpose of the Study:
- To establish and characterize the first quantitative animal model for S. agalactiae osteomyelitis.
- To compare the pathogenic mechanisms and tissue tropism of S. aureus and S. agalactiae in implant-associated osteomyelitis.
- To elucidate the distinct modes of bone colonization by these two bacterial species.
Main Methods:
- Comparison of S. aureus and S. agalactiae in a murine model of implant-associated osteomyelitis.
- In vitro analysis using scanning electron microscopy and CFU quantification for bacterial inocula.
- In vivo assessment including body weight, CFU counts, X-ray, micro-CT, histology, and transmission electron microscopy.
Main Results:
- S. aureus exhibited greater virulence than S. agalactiae, with more severe osteolysis and implant loosening.
- S. agalactiae infections resulted in less bone destruction and fewer osteoclasts compared to S. aureus.
- Transmission electron microscopy revealed S. agalactiae colonizes blood vessels (vasculotropic), while S. aureus colonizes the osteocyte network (osteotropic).
Conclusions:
- This study successfully established the first quantitative animal model for S. agalactiae osteomyelitis.
- S. agalactiae demonstrates a vasculotropic infection strategy in bone, distinct from the osteotropic strategy of S. aureus.
- Understanding these distinct pathogenic behaviors is crucial for developing targeted treatments for different types of osteomyelitis.
