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Published on: March 14, 2019
Bacterial exposure required to induce rabbit calvarial bone graft infection by superficial contamination
J F Lalikos1, M P Mooney, J Janosky
1Division of Plastic, Reconstructive and Oral-Maxillofacial Surgery, University of Pittsburgh Medical Center, Pennsylvania.
Abstract:
Little is known about the minimum bacterial dose required to induce infections by superficial contamination alone (i.e., not direct inoculation). This study quantified superficial rabbit calvarial bone graft contamination by exposing parietal bone grafts to Staphylococcus aureus. Two 5 x 5-mm full-thickness calvarial bone grafts were harvested from 40 rabbits and contaminated with different concentrations (range = 10(7)-10(11) colony-forming units [CFUs]/mL) of S. aureus by immersion. One graft from each rabbit was cultured immediately, and the other was inset into a calvarial donor site, fixed in place with wire, and observed for evidence of infection. At harvest (28 days postoperatively), a bacterial exposure of greater than 10(8) CFUs/mL of S. aureus was required to induce infections in the rabbit calvarial grafts (p < 0.001, Student's t-test), transmitting an infectious dose of approximately more than 10(4) CFUs per graft. These results validate the previously known dogma regarding the number of organisms needed to manifest infection [1,2] and highlight a multifold increment in bacterial count needed to transmit this infectious dose by superficial contamination alone. Such a model may be useful in investigating the efficacy of various treatment modalities of contaminated bone.
Insights
A minimum bacterial dose exceeding 10(8) colony-forming units (CFUs)/mL of Staphylococcus aureus is necessary to cause infection via superficial contamination of rabbit calvarial bone grafts. This highlights a significantly higher bacterial threshold for infection transmission through incidental contact.
Area of Science:
- Orthopedics
- Infectious Disease
- Microbiology
Background:
- Superficial contamination's role in bone graft infections is poorly understood.
- Establishing minimum bacterial infectious doses is crucial for preventing implant-associated infections.
Purpose of the Study:
- To quantify the minimum bacterial dose of Staphylococcus aureus required to induce infection in rabbit calvarial bone grafts through superficial contamination.
- To establish a reliable animal model for studying superficial bacterial contamination of bone grafts.
Main Methods:
- Harvested 80 full-thickness rabbit calvarial bone grafts (5x5mm).
- Contaminated grafts with varying concentrations of Staphylococcus aureus (10(7)-10(11) CFUs/mL) via immersion.
- Implanted one graft per rabbit into a calvarial donor site and observed for 28 days.
- Cultured remaining grafts immediately post-contamination.
Main Results:
- A bacterial concentration greater than 10(8) CFUs/mL of Staphylococcus aureus was required to induce infection in calvarial bone grafts.
- This corresponds to an infectious dose of approximately more than 10(4) CFUs per graft.
- A statistically significant difference (p < 0.001) was observed in infection rates based on bacterial exposure levels.
Conclusions:
- Superficial contamination requires a substantially higher bacterial load than direct inoculation to cause bone graft infection.
- The findings support existing knowledge on infectious doses while emphasizing the increased threshold for superficial contamination.
- This rabbit calvarial model can be utilized to evaluate treatments for contaminated bone grafts.
