Forsøksdyr: The ability of sonication as a method to dislodge biofilm embedded Staphylococcus epidermidis from orthopedic implants

Godkjenningsdato 31.01.2020

Godkjenningsperiode 31.01.2020-31.01.2022

Development of prosthetic joint surgery is one of the major successes in medicine over the last century. But there is a catch: Prosthetic Joint Infection (PJI) is a devastating complication after prosthetic surgery. Culture of harvested tissue biopsies during prosthetic revision is commonly used when diagnosing a PJI, but the sensitivity of bacterial cultivation of tissue samples is not optimal. It has been claimed that sonication (high frequency ultrasound) of explanted prostheses with subsequent culturing of sonication fluid can increase the sensitivity of the test compared to culturing of tissue samples. However, these results have not been unambiguously reproducible.
We suspected that sonication, as a method to dislodge biofilm in general, might not be as effective as current opinion suggests. We have carried out an in vitro-study to investigate the effectiveness of sonication as a method to dislodge biofilm embedded S. epidermidis from a steel surface. We used epifluorescence microscopy to visualize the surface of steel plates with established biofilm before and after sonication. The results show a highly variable effect. Our conclusion is that the ability of sonication to dislodge biofilm embedded S. epidermidis in vitro is highly variable. This study of how biofilm respond to sonication elucidate important aspects about the application of sonication as an indirect quantitative method, utilized in a vast body of research. Investigation of the effect of sonication on in vivo biofilms will add highly valuable knowledge about the effect of sonication when diagnosing PJI in clinical settings.

Previous experience with identical experimental setup where bone allografts are placed in a sub-fascial pouch on the back of the animals indicate mild harm to the animals. A pain score sheet showed lowest possible score, indicating no distress. This was in accordance with observations of the animals in the housing facility.

Expected benefits:
We hope to gain clinically relevant knowledge of how in vivo biofilm respond to sonication. This event is highly dependent on in vivo maturation of biofilm and host immune response. Furthermore, evidence of biofilm attached to explanted orthopedic implants is mere anecdotal as the surface of prostheses are practically impossible to visualize microscopically.

Number of animals and species: 11 rodents, Rattus norvegicus (Albino outbred Wistar).

We have carried out in vitro-experiments that show a variable effect of sonication. Biofilm formation is highly dependent on in vivo maturation and host immune response. The qualities of an in vivo biofilm is very different from in vitro biofilm and we expect to gain important knowledge relevant to biofilm observed in clinical implant infections.

The experiment establish a chronic infection around a bone allograft with no visual wound infection and minimal distress to the animals. No further intervention is done until the end of the experiment where the animals are euthanized during general inhalation anesthesia.

A power analysis based on in vitro results determine minimal number of animals needed. The model facilitate four parallel specimens (biofilm covered steel plates) per animal, which is further reducing the number.