Immunosuppression augments growth of graft-adherent Staphylococcus epidermidis

Abstract

Objective: To determine if systemic suppression of host defenses during graft implantation alters the initial adherence and subsequent growth of Staphylococcus epidermidis on vascular prostheses.

Design: Dacron grafts 1 cm2 were implanted in the back subcutaneous tissue of Swiss-Webster mice (n = 247), followed by topical inoculation with 2 x 10(7), 2 x 10(5), 2 x 10(3), or 2 x 10(1) colony-forming units of S epidermidis. Half of the mice were immunosuppressed with cyclophosphamide (150 mg/kg intraperitoneally), to achieve a consistent, significant decrease in the white blood cell count and major histocompatibility complex class II (Ia) expression. Control mice received an equal volume of saline solution. Graft bacterial biofilm concentrations were determined at 1 day for adherence and within 2 weeks for bacterial growth, by using sonication and quantitative agar culture.

Results: Immunosuppression did not significantly alter the initial adherence of bacteria to vascular grafts. Immunosuppressed animals that were inoculated with 2 x 10(7) and 2 x 10(5) colony-forming units of S epidermidis had significantly higher bacterial biofilm concentrations as compared with those in control animals. Graft infection persisted at 14 days in all animals, with and without immunosuppression.

Conclusions: Suppression of immune function during graft implantation augmented growth of adherent bacteria. The effect of short-term perioperative immunosuppression on late-appearing S epidermidis graft infection needs further study.