Microbiological diagnosis of aortofemoral graft infections

Abstract

Vascular surgery has benefitted from the introduction and development of new biomaterials used in grafting. However, these prosthetic materials are at risk of infection. 1-4 Such infections occur both early after implantation of grafts, and much later as a consequence of different mechanisms. 5 Early onset graft infections, occurring within 4 months of implantation, are often a consequence of inadequate aseptic surgical procedures or of inadequate patient selection procedures. 5-7 Late onset infections, occurring many years after implantation, are generally due to bacteria spreading from contiguous intestinal sites or through the blood stream. 8'9 Although virtually any microorganism can cause a vascular graft infection, the most frequently isolated bacteria are staphylococci (both Staphylococcus aureus and coagulase-negative Staphylococcus spp.) and enterobacteria (principally Escherichia coli), though enterococci and Pseudomonas aeruginosa are also frequently isolated. 1~'~°'1~ According to several in vitro findings the physical nature of different biomaterials shows some influence on bacterial adhesion rates, expanded polytetrafluoroethylene being less suitable for bacterial adhesion than dacron, though the significance of such findings for the in vivo susceptibility to colonisation is still not completely understood. ~2-14 Collagen or gelatin impregnated grafts also appear to be more resistant. Two principal characteristics of such infections contribute to their severity: the almost complete absence of specific clinical signs, particularly in the early phases (diagnosis is almost always possible when pus is already partially or totally surrounding the graft or causing a fistula), and their extreme resistance to chemotherapy, due to the bacterial production of esopolymeric substances. 1°'~5 Both these aspects point out the absolute necessity for diagnostic procedures that