Staphylococcus epidermidis is cleared from biomaterial implants but persists in peri-implant tissue in mice despite rifampicin/vancomycin treatment

Infections associated with implanted biomedical devices (BAI) are predominantly caused by Staphylococcus epidermidis. We previously observed in murine experimental BAI that S. epidermidis persists in peri-implant tissue rather than on the implanted biomaterial itself (Boelens et al., J Infect Dis 2000;181:1337-1349; Broekhuizen et al., Infect Immun 2007;75:1129-1136). To investigate the efficacy of rifampicin/vancomycin to clear S. epidermidis from implants and peri-implant tissues, mice with two implants were challenged with 10(7) cfu S. epidermidis per implant and received daily injections of rifampicin (25 mg/kg) and vancomycin (50 mg/kg). On the day of termination, implants and peri-implant tissue were collected and processed for culture and histology. After 1 and 8 days, implants of control mice were culture positive in 14/18 and 5/16 cases, respectively, and tissue biopsies were all culture positive. In the antibiotic-treated mice, bacteria were recovered from only 1/18 and 1/16 implants after 1 and 8 days, respectively, whereas the tissues were culture positive in 14/18 and 7/16 biopsies, respectively. In microscopy, bacteria were seen in the tissue at a distance of several cell layers from the tissue-implant interface, colocalized with host cells. Thus, although a regimen of rifampicin/vancomycin sterilized the implants, S. epidermidis persisted in peri-implant tissue, which might be an as yet unrecognized reservoir in the pathogenesis of BAI