Ica-expression and gentamicin susceptibility of Staphylococcus epidermidis biofilm on orthopedic implant biomaterials

Ica-expression by Staphylococcus epidermidis and slime production depends on environmental conditions such as implant material and presence of antibiotics. Here, we evaluate biofilm formation and ica-expression of S. epidermidis strains on biomaterials involved in total hip- and knee arthroplasty [polyethylene (PE), polymethylmethacrylate (PMMA), stainless steel (SS)]. Ica-expression, assayed using real-time RT-PCR, was highest on PE as confirmed using confocal laser scanning microscopy. Yet biofilm formation by S. epidermidis was most extensive on SS, with less slime production. Ica-expression and slime production were minimal on PMMA. After 3 h of continued growth of 24 h old biofilms in the presence of gentamicin, biofilms on PE showed lower susceptibility to gentamicin, relative to the other materials, presumably as a result of the stronger ica-expression. A higher gentamicin concentration further decreased metabolic activity on all biomaterials. It is concluded that the level of biomaterial-induced ica-expression does not correlate with the amount of biofilm formed, but initially aids bacteria in surviving antibiotic attacks. Once antibiotic treatment has started however, also the antibiotic itself induces slime production and only if its concentration is high enough, killing results. Results suggest that biomaterial-associated infections in orthopedics by S. epidermidis on PE may be more difficult to eradicate than on PMMA or SS.