Influence of staphylococcus epidermidis on collagen crimp patterns of soft tissue allograft

Abstract

Background: postoperative infections, commonly from Staphylococcus epidermidis, may result in anterior cruciate ligament (ACL) graft failure and necessitate revision surgery. In biomechanical studies, S. epidermidis has been shown to establish biofilms on tendons and reduce graft strength.

Purpose: the goal of this study is to determine the impact of bacterial bioburden on the collagen structure of tendon. We hypothesized that an increase in S. epidermidis biofilm will compromise tendon crimp, a pattern necessary for mechanical integrity, of soft tissue allografts.

Study design: controlled laboratory study.

Methods: cultures of S. epidermidis were inoculated on tibialis anterior cadaveric tendons. Conditions assessed included 5 x 105 CFUs (colony-forming units) or concentrated spent media from culture (no living bacteria). Incubation times of 30 minutes, 3 hours, 6 hours, and 24 hours were utilized. Second-harmonic generation microscopy allowed for visualization of collagen autofluorescence. Crimp lengths were determined with ImageJ and compared based on incubation time. Incubation time positively correlated with increasing S. epidermidis bioburden.

Results: 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 significant fine crimp lengthening occurred after 6 hours (p=<0.0001). No changes in crimp length were identified following incubation media lacking living bacteria.

Conclusions: the results of this study demonstrate that exposure to S. epidermidis biofilms negatively impact collagen crimp structure. Structural alterations at the collagen fiber level occur within 30 minutes of exposure to media containing S. epidermidis.

Key terms: S. epidermis; tendon; allograft; bacterial bioburden; collagen fiber.

What is known about the subject: previous research has explored the relationship between S. epidermidis biofilms and ACL graft strength by testing the mechanical integrity of tibialis posterior tendon grafts. Following incubation of S. epidermidis (10000 CFU/ml), the Young’s modulus of elasticity of the grafts significantly decreased resulting in increased compliance, and increasing bioburden was also associated with decreased tensile strength.

What this study adds to existing knowledge: 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 within 30 minutes of exposure and before gross changes can be appreciated, which highlights the need for antimicrobial precautions to prevent graft colonization and maximize graft mechanical strength.

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Identifiers

ORCID for Paul Stoodley: orcid.org/0000-0001-6069-273X

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