Method

We tested six clinically important biomaterials: cobalt chrome alloy, pure titanium, grid-blasted titanium, porous plasma-coated titanium with/without hydroxyapatite, and polyethylene. Two laboratory strains of bacteria commonly causing PJI were used, namely Staphylococcus aureus* and Staphylococcus epidermidis*. After overnight incubation with biofilm formation, the test samples were washed and individually exposed to increasing daptomycin concentrations (4–256 mg/l) during 24-hours. Samples were subsequently sonicated in order to detect dislodged biofilm bacteria on blood agar plates by viable growth and transferred to a microcalorimeter*** for real-time measurement of growth related heat flow during 24-h incubation. Minimal biofilm eradication concentration (MBEC) was determined as the lowest concentration of antibiotic required to eradicate the biofilm bacteria on the sample.

The time to detection expressed as the heat flow >50 µW (TTD-50) indirectly quantifies the initial amount of biofilm bacteria, with a shorter TTD-50 representing a larger amount of bacteria.