Friday, April 28, 2017

What does an infected biofilm on a titanium implant look like?

Quantification of Peri-Implant Bacterial Load and in Vivo Biofilm Formation in an Innovative, Clinically Representative Mouse Model of Periprosthetic Joint Infection

These authors developed a murine PJI model involving a Ti-6Al-4V implant capable of bearing weight and permitting quantitative analysis of periprosthetic bacterial load and evaluation of biofilm.

Twenty-five mice received a unilateral proximal tibial implant and intra-articular injection of either Staphylococcus aureus containing saline or saline solution alone.

In contrast to the control mice, infected mice had difficulty walking over time, exhibited radiographic findings of septic implant loosening, and had significantly elevated inflammatory markers. Periprosthetic tissues and implant surfaces contained viable S. aureus.

Images of a pristine implant, showing the smooth tibial baseplate that resides in the articular space and the stem that resides in the intramedullary space, roughened with sintered titanium beads (arrows).

Below left - an implant retrieved from an infected animal 2 weeks following surgery, with bacteria visible adjacent to a titanium bead (star). Below right - magnified view of the boxed region of interest, showing clusters of S. aureus bacteria covered in biofilm consisting of several fibrin-like shapes, including straight fibers connecting bacteria (arrows).

Below left - an implant retrieved from an infected animal 6 weeks following surgery, showing adherent material consisting of cellular and fibrinous content. Below right - magnified view of the implant, showing a cluster of S. aureus bacteria covered in biofilm in the middle of the image, as well as a wall of fibrinous tissue filled with multiple layers of bacteria (arrows).

Below left - image from an infected implant 6 weeks following surgery, showing multiple host cells (arrowheads) covering titanium beads (stars) and the fibrin coating. Below right - magnified view of the same implant showing 3 S. aureus bacteria (arrows) surrounded by host leukocytes (yellow asterisks). A red blood cell is also noted in the field (red asterisk).

Comment: While these images are from an animal model infected with S. aureus, they are helpful reminders of how adherent bacteria can be to a Titanium implant surface. It is no wonder that such colonization cannot be resolved with systemic or local antibiotics. Implant exchange is the key.

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