Prosthetic joint infections are difficult to treat due to bacterial biofilm. Our group has developed a linezolid elution system by human cancellous bone delivering high concentrations the first 48 hours (Giannitsioti et al. 53rd ICAAC, 2013: A-1050). We tested the activity of this system to inhibit growth of one ica expressing isolate of Staphylococcus epidermidis (MRSE).

At a first step, sterile mesh cylinders containing bone particles of the femoral head of healthy volunteers (MCB) were impregnated into 3mg/ml linezolid for 1, 24 and 48 hours. Then log-phase inocula of 103, 105 and 107cfu/ml were exposed to MCB at 370C for 8 days with regular readings of bacterial growth. MCB were transferred into fresh Muller-Hinton Broth (MHB) every 24h to avoid material corrosion. At a second step, to simulate the ability of the system against biofilm-coated MCB, MCB without linezolid were incubated with 103 and 105 cfu/ml for 1 and 24h. MCB were daily transferred into fresh MHB containing 100μg/ml on day 1, 15 μg/ml on day 2, 3 μg/ml on day 3 and 0.5 μg/ml on day 4.

24h linezolid impregnated MCB achieved rapid bacterial killing of the 105 cfu/ml bacterial suspension followed by re-growth (Figure, n= 5). Similar results were observed for 1h and 48h impregnation and for both tested inocula. When biofilm-coated MCB generated by 24h exposure to 105 cfu/ml were exposed to linezolid, rapid bacterial killing was achieved followed by re-growth.

Linezolid local elution may inhibit biofilm-producing MRSE only when locally eluted concentrations exceed 10μg/ml.