Immunosuppression augments growth of graft-adherent Staphylococcus epidermidis
T. M. Bergamini, R. A. Corpus Jr, T. M. McCurry, J. C. Peyton, K. R. Brittian and W. G. Cheadle
Department of Surgery, University of Louisville, Ky, USA.
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.
