Bacteremic infectability of vascular grafts: An experimental study

The present study was undertaken with the aim of defining the differences, if any, in bacteremic infectability of some currently available arterial grafts. The following prostheses were investigated: two kinds of expanded polytetrafluoroethylene (PTFE); Dacron knitted double velour; Dacron knitted pretreated with gelatin. Forty beagle dogs were used. In each animal the infrarenal aorta was resected and replaced by means of Φ.6 mm segment of: PTFE type I 10 dogs; PTFE type II 10 dogs; Dacron knitted double velour 10 dogs; Dacron knitted pretreated with gelatin 10 dogs. At the end of the operation, each animal was administered IV with 100 mL of normal saline containing a suspension of Staphylococcus aureus coagulase-positive phage type 5504. The bacterial load was 10⁵ in 5 animals of each group, 10⁷ in the remaining 5. The graft was retrieved after forty-five days and studied in the microbiology laboratory (study of graft homogenate) and in the pathology laboratory (study by conventional microscopy of graft healing). When culture yielded a strain of Staph. aureus, this was retyped for phage 5504 specificity. All grafts were patent at the end of the experiment: partial thrombosis was, however, observed, coupled with a frank perigraft inflammation in: 3 PTFE type 1 (2 Staph.10⁵, 1 Staph.10⁷); 1 PTFE type 2 (Staph. 10⁵); 1 Dacron knitted double velour (Staph. 10⁷). Baterial colonies within the graft tissue were evident at microscopy in 4 PTFE grafts and in 1 gelatin-pretreated graft. Culture was positive and specific in all the gelatin-treated Dacron grafts and in 60% of the nonpretreated Dacron and PTFE grafts. An optimal result (good healing, no inflammation, no infection) was observed only in 3 PTFE and in 2 'conventional' Dacron grafts. The possibility is suggested that bacteria may be harbored in graft tissue without any clinically evident effect; moreover, some late graft infection could be attributable to an early bacteremic contamination.