Fibrinolytic and antibiotic treatment of prosthetic vascular graft infections in a novel rat model

by Mikkel Illemann Johansen, Søren Jensen Rahbek, Søren Jensen-Fangel, Gabriel Antonio S. Minero, Louise Kruse Jensen, Ole Halfdan Larsen, Lise Tornvig Erikstrup, Anders Marthinsen Seefeldt, Lars Østergaard, Rikke Louise Meyer, Nis Pedersen Jørgensen

We developed a rat model of prosthetic vascular graft infection to assess, whether the fibrinolytic tissue plasminogen activator (tPA) could increase the efficacy of antibiotic therapy.

Rats were implanted a polyethylene graft in the common carotid artery, pre-inoculated with approx. 6 log¹⁰ colony forming units (CFU) of methicillin resistant Staphylococcus aureus. Ten days after surgery, rats were randomized to either: 0.9% NaCl (n = 8), vancomycin (n = 8), vancomycin + tPA (n = 8), vancomycin + rifampicin (n = 18) or vancomycin + rifampicin + tPA (n = 18). Treatment duration was seven days. Approximately 36 hours after the end of treatment, the rats were euthanized, and grafts and organs were harvested for CFU enumeration.

All animals in the control group had significantly higher CFU at the time of euthanization compared to bacterial load found on the grafts prior to inoculation (6.45 vs. 4.36 mean log¹⁰ CFU/mL, p = 0.0011), and both the procedure and infection were well tolerated.Vancomycin and rifampicin treatment were superior to monotherapy with vancomycin, as it lead to a marked decrease in median bacterial load on the grafts (3.50 vs. 6.56 log¹⁰ CFU/mL, p = 0.0016). The addition of tPA to vancomycin and rifampicin combination treatment did not show a further decrease in bacterial load (4.078 vs. 3.50 log¹⁰ CFU/mL, p = 0.26). The cure rate was 16% in the vancomycin + rifampicin group vs. 37.5% cure rate in the vancomycin + rifampicin + tPA group. Whilst interesting, this trend was not significant at our sample size (p = 0.24).

We developed the first functional model of an arterial prosthetic vascular graft infection in rats. Antibiotic combination therapy with vancomycin and rifampicin was superior to vancomycin monotherapy, and the addition of tPA did not significantly reduce bacterial load, nor significantly increase cure rate.