Scripties UMCG - Rijksuniversiteit Groningen
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Researching the use of bacteria-targeting fluorescent tracers to accurately detect prosthetic joint infections in an early stage

(2018) Schoenmaker, J.W.A.

A prosthetic joint infection (PJI) is one of the most serious complications following a total joint replacement. Early and accurate diagnosis of PJIs is necessary to increase the chance for successful treatment with surgical debridement and antibiotic therapy. A relatively novel approach which can potentially achieve this goal is fluorescent optical imaging.
The purpose of this thesis was to research two novel ways to detect PJIs in early stage with the use of bacteria-targeting fluorescent tracers.
The first project (project 1) assesses if fluorescently labelled vancomycin (vanco-800CW) can be used to arthroscopically visualize an infected prosthesis. To determine the feasibility of this approach, it will be tested on a post-mortem knee joint model.
The second project (project 2) researches the potential of a fluorescent tracer, the P2&3 TT Probe, to detect haematogenous spread of Staphylococcus aureus via the micrococcal nuclease (MN) enzyme.
Materials and methods:
Project 1. All the required in vitro experiments and the set-up for a post-mortem experiment were conducted. First, a protocol for growing S. aureus and Staphylococcus epidermidis (Coagulase-Negative Staphylococci) biofilms on implants was created and optimized. Subsequently, several in vitro experiments were conducted in which biofilm-coated and uncoated implants incubated with vanco-800CW were visualized. For imaging the IVIS Lumina II (Caliper Life Science, Hopkinton, United States) and the Cellvizio fluorescence endomicroscopy system (Mauna Kea Technologies, Paris, France) were used. To assess if biofilm-coated implants incubated with vanco-800CW emitted more fluorescent signal than uncoated implants or implants not incubated with vanco-800CW, a statistical analysis (Mann-Whitney U test) was performed.
Project 2. Blood culture samples were collected from the diagnostics microbiology laboratory of the University Medical Center Groningen. Both samples and control samples with buffer were treated with the P2&3 TT Probe and evaluated for MN activity.
Project 1. S. aureus and S. epidermidis biofilms could be grown on implants. Biofilm-coated implants incubated with vanco-800CW (Mdn = 338.4) emitted significantly more fluorescent signal than uncoated implants incubated with vanco-800CW (Mdn = 64.0), U = 0, p<0.001 or implants not incubated with vanco-800CW (Mdn = 33.4), U = 0, p<0.001. The Cellvizio fluorescence endomicroscopy system was not able to distinguish biofilm-coated implants from uncoated implants. Due to this latter result, the post-mortem arthroscopies were cancelled.
Project 2. 34 blood culture samples were analysed. 17 of those samples were infected with S. aureus, 8 samples were infected with another bacterial pathogen and 9 samples were uninfected.
All the normalized fluorescent signals of the individual blood culture samples infected with S. aureus were greater than the normalized fluorescent signals of the individual samples without S. aureus.
Arthroscopic detection of PJIs in an early stage using vanco-800CW can potentially be achieved in the near future. With adjustments in imaging modality, post-mortem experiments will prove if this method succeeds. Detection of S. aureus in blood cultures using the P2&3 TT Probe is feasible. This offers the possibility of early diagnosis of S. aureus bacteriaemia, a condition that is highly associated with PJIs. Moreover, this optical tracer might be similar effective in detecting S. aureus in aspirated joint fluid, or even inside the infected joint itself. Further research needs

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