An ex vivo study of infections of vascular grafts and endografts with scanning electron microscopy.

BACKGROUND: Vascular graft and endograft infections (VGEIs) are complicated by high morbidity, mortality, and recurrence rates, notably due to biofilm formation on the graft surface, hardly dislodgeable by the sole anti-infectious treatment. The characteristics of this biofilm are still poorly documented. The aim of this study was to evaluate ex vivo biofilm on removed infected vascular grafts and endografts (VGEs).

METHODS: Explanted VGEs were prospectively collected from 2019 to 2022 at Bordeaux University Hospital, France. Two samples per graft were used for scanning electron microscopy imaging, one was sonicated and both grafts' sides were imaged.

RESULTS: A total of 26 patients were included, 18 with VGEI, eight without any infection (endoleak and/or thrombosis) and 29 VGEs were collected. Microbial documentation was obtained in 83% of VGEIs. A thick layer of fibrin was visible on almost all grafts, mixed with a dense biofilm matrix on infected grafts visible as early as one month after the onset of infection. Bacteria were not always visualized on infected grafts' surface (80% on outer side and 85% on luminal side) but were surprisingly present on a third of non-infected grafts. There was no significant difference between biofilm, fibrin, and microorganisms' distribution between the two grafts' sides. However, there were clear differences between infected and non-infected grafts, since immune cells, bacteria and biofilm were more frequently visualized on both sides of infected grafts (p<.05). Bacteria and immune cells although still visible, were significantly less present after sonication; the number of other elements including biofilm was not significantly different.

CONCLUSIONS: The persistence of a thick layer of fibrin and biofilm embedding microorganisms on both sides of infected VGE even after one month of infection could be the explanation for the low success rates of conservative management and the usual need for graft removal to treat VGEIs.