Tissue colonization from implantable biomaterials with low numbers of bacteria

This study was undertaken to evaluate the risk of infection (defined as the recovery of the relevant organism from the implant site) in a mouse model when low numbers of bacteria were present on an implanted biomaterial. Segments of different types of suture with adherent bacteria were implanted subcutaneously into mice. The infection risk with Staphylococcus aureus was greater than with Staphylococcus epidermidis RP62A or Candida albicans. The infection risk with the implantation of multifilament sutures was significantly greater than with monofilament sutures. When <10 colony forming units (cfu) of S. aureus were present on monofilament suture material, the infection rate was 3%. When <10 cfu of S. aureus were present on multifilament suture material, the infection rate was 7%. An infection rate of 15% occurred with <10 cfu of S. aureus on multifilament nylon sutures. When >10 but <20 cfu of S. aureus were present, the infection rates were 4 and 51%, respectively. These data confirm that the infection rate with multifilament sutures (or porous materials) is greater than with monofilament sutures (or solid materials) when the organisms are encountered at implantation (acute model) and indicate that a significant risk of infection may occur when only a few organisms are on a device at implantation.