Clinical behavior of implant infections due to Staphylococcus epidermidis

Surgical implants and other foreign material are increasingly used in modern medicine to restore or to improve the function of the human body. Infection of an implant is associated with considerable morbidity due to frequent hospitalizations, surgery and antimicrobial treatment. The underlying mechanism is the formation of a bacterial biofilm on the surface of the implanted body. The recognition and diagnosis of implant infections is essential for further therapy and, above all, the decision to remove and exchange the implant.

We compared the data of 60 patients with implant infections with those of 60 patients with transient bacteremia caused by Staphylococcus epidermidis. The pathogens isolated from blood were characterized with regard to antimicrobial susceptibility and formation of biofilms using a static microtiter plate model. Wild type skin isolates from non-hospitalized healthy volunteers served as control with regard to antimicrobial susceptibility and biofilm formation.

Clinical signs and symptoms, underlying diseases and outcome were not different in either group. However, patients with implant infection had fever over a longer time (mean 12 days versus 3 days, respectively, p < 0.05) and more often positive blood cultures than patients with transient bacteremia (3.1 versus 1.2, p < 0.05). Thrombocytopenia was observed in patients with implant infections but not in patients with transient bacteremia (p < 0.05). Biofilms were formed in 86.4 % of the isolates in implant infection, in 88.8 % in transient bacteremia and in 76.9 % of the isolates from healthy volunteers (not significant). Multi-resistance to penicillin, oxacillin, erythromycin, clindamycin, ciprofloxacin and trimethoprim was more common in the hospital strains than in the wild type strains (75.6 % versus 48.7 %, p < 0.05).

The clinical features of implant infections are indistinguishable from those of transient bacteremia. Persisting fever and multiple blood culture yielding the growth of skin flora bacteria are strong indicators for infection of implanted material. Biofilm formation and antimicrobial multi-resistance, as common in implant infection as in transient bacteremia, seem to be accessory factors in infections due to Staphylococcus epidermidis.