Analysis of linezolid and tigecycline as candidates for local prophylaxis via antibiotic-loaded bone cement.

OBJECTIVES: To assess the Gram-positive-specific antibiotic linezolid and the broad-spectrum antibiotic tigecycline for use in local antibiotic delivery via antibiotic-loaded bone cement. METHODS: Linezolid and tigecycline were added to Biomet bone cement at varying concentrations. Antibiotic elution over 1 week was quantified by HPLC-MS. The effect of wear on elution over 51 h was determined using a modified TE-66 wear tester. Eluted antibiotics were used to determine the MICs for a panel of clinically relevant bacteria. The impact strength of antibiotic-loaded samples was determined using a Charpy-type impact testing apparatus. Cytotoxicity of eluted antibiotics against MG-63 cells was evaluated using an MTT assay. RESULTS: Linezolid and tigecycline eluted from bone cement to clinically relevant levels within 1 h and retained activity over 1 week. Mechanical wear significantly reduced elution of tigecycline, but had little effect on elution of linezolid. Linezolid showed low cytotoxicity towards MG-63 cells with ≤300 mg/mL resulting in >50% cell activity. Cytotoxicity of tigecycline was higher, with an IC50 of 5-10 mg/L. CONCLUSIONS: Linezolid and tigecycline retain activity after elution from bone cement. The concentration of tigecycline may need to be carefully controlled due to cytotoxicity. The effect of wear on bone cement may need to be considered if tigecycline is to be used for local delivery. Up to 10% linezolid can be added without affecting the impact strength of the bone cement. These results are promising indications for future investigation of these antibiotics for use in local antibiotic delivery strategies.

Electricity generation from wastewaters with starch as carbon source using a mediatorless microbial fuel cell.

Microbial fuel cells represent a new method for producing electricity from the oxidation of organic matter. A mediatorless microbial fuel cell was developed using Escherichia coli as the active bacterial component with synthetic wastewater of potato extract as the energy source. The two-chamber fuel cell, with a relation of volume between anode and cathode chamber of 8:1, was operated in batch mode. The response was similar to that obtained when glucose was used as the carbon source. The performance characteristics of the fuel cell were evaluated with two different anode and cathode shapes, platinised titanium strip or mesh; the highest maximum power density (502mWm(-2)) was achieved in the microbial fuel cell with mesh electrodes. In addition to electricity generation, the MFC exhibited efficient treatment of wastewater so that significant reduction of initial oxygen demand of wastewater by 61% was observed. These results demonstrate that potato starch can be used for power generation in a mediatorless microbial fuel cell with high removal efficiency of chemical oxygen demand.

Contrasting effects of physical wear on elution of two antibiotics from orthopedic cement.

The use of antibiotics as a supplement to bone cement for the purposes of providing a local release of antibiotics is common practice in arthroplasty surgery and the kinetics of elution of the antibiotics in such systems have been investigated previously. However, in these previous studies no account was taken of the potential effects that wear may have on the elution kinetics of the antibiotic. Here, we have modified an existing wear testing rig to allow the simultaneous study of the elution kinetics of bone cement samples containing antibiotics being subjected to immersion only and immersion and conjoint wear. The results show contrasting effects with two commonly used antibiotics. Bone cement containing daptomycin showed no substantial change in antibiotic elution due to wear, while cement containing gentamicin (the most commonly used antibiotic in this application) in contrast demonstrated a substantial reduction in the rate of antibiotic elution when wear was applied. Scanning electron microscopy revealed a possible explanation for these diverse results, due to wear-induced "sealing" of the surface in conjunction with the crystal morphology of the antibiotic.