Protamine sulfate and vancomycin are synergistic against Staphylococcus epidermidis prosthesis infection in vivo

We have previously demonstrated that the quaternary amine, protamine sulfate (PS), is bactericidal against Staphylococcus epidermidis. In an attempt to decrease genitourinary prosthesis infection rates, we examined the ability of PS as a wound irrigant to inhibit Staphylococcus epidermidis viability. Eighty-seven Sprague-Dawley rats were studied by implanting a sterile silicone pellet in their dorsum. The pellet was inoculated with Staphylococcus epidermidis and the rats were divided into four groups based on the wound irrigant employed after inoculation: (1) control (sterile water) (2) vancomycin; (3) PS; (4) vancomycin + PS. All rats received perioperative and daily intramuscular vancomycin, and the pellets were explanted on postoperative day 28 and cultured. The infection rates were: (1) control 77%, (2) vancomycin 50%, (3) protamine sulfate 67%, and (4) protamine sulfate and vancomycin 19%. The differences between (2) vancomycin versus (4) vancomycin + PS and (3) PS versus (4) vancomycin + PS were significant (p = 0.05 and p < 0.005). The data suggest that PS potentiates vancomycin as a wound irrigant in prosthesis implantation.