Summary

The results of this study demonstrate that S. epidermidis biofilms negatively impact collagen crimp structure and suggest that a bacterial metabolite may aid in this process, highlighting the need for antimicrobial precautions to prevent graft colonization and maximize graft mechanical strength.

Abstract

Objective

The goal of this study was to determine the impact of bacterial bioburden on the collagen structure of tendon to explain the biofilm effect of reduced graft strength. Anterior cruciate ligament (ACL) reconstruction is a common knee procedure, and complications can result in adverse patient outcomes. Postoperative infections, commonly from Staphylococcus epidermidis, may directly alter the integrity of the reconstructed graft. In biomechanical studies, S. epidermidis has been shown to establish biofilms on allograft tendons and reduce graft strength through increased elasticity. We hypothesized that an increase in S. epidermidisbiofilm will compromise tendon crimp, a waveform pattern necessary for mechanical integrity, of ACL allografts.

Methods

Cultures of S. epidermidis were inoculated on tibialis anterior cadaveric tendons to illicit biofilm growth. Conditions assessed included 5 x 105 CFUs or concentrated spent media from culture and incubation times of 30 minutes, 3 hours, 6 hours, and 24 hours. Second-harmonic generation microscopy allowed for visualization of collagen autofluorescence. Crimp lengths were determined with ImageJ. ANOVA analyses and t-tests were utilized with an alpha of 0.05 deemed statistically significant.

Results

Incubation time positively correlated with increasing S. epidermidis bioburden. Additionally, macroscopic changes in projected tendon surface area were observed significantly following 6 hours of incubation. Both fine and coarse crimp patterns lengthened with increasing incubation time. Significant coarse crimp changes were observed after only 30-minute incubations (p=<0.029), whereas fine crimp lengthened significantly after 6 hours (p=<0.0001). No trend in crimp lengthening was identified following incubation in media after bacterial removal.

Conclusion

The results of this study demonstrate that S. epidermidis biofilms negatively impact collagen crimp structure and suggest that a bacterial metabolite may aid in this process. In the presence of S. epidermidis, structural alterations at the collagen fiber level occur quickly and before gross changes can be appreciated, which highlights the need for antimicrobial precautions to prevent graft colonization and maximize graft mechanical strength.