Thermal Eradication of Prosthetic Joint Associated Bacteria

PURPOSE: As with other medical implants, prosthetic joints provide a hospitable surface for bacterial adherence and biofilm formation. We are developing a non-invasive thermal technique to destroy biofilm on the metal surfaces of prosthetic joints using alternating magnetic fields (AMF). One hypothesized benefit of AMF therapy is that it could be used in conjunction with traditional antibiotics to produce a synergistic bactericidal effect. The purpose of this study is to characterize the thermal sensitivity of bacteria in the presence of antibiotics to aid in the development of appropriate parameters for AMF dosing. METHODS: Planktonic solutions of Pseudomonas aeruginosa were thermally shocked in heating blocks with and without minimum inhibitory concentrations of ciprofloxacin. Bacterial solutions were plated on blood agar at intervals throughout the experiment to create a time-kill curve of the combined effects of heat shock therapy and ciprofloxacin. RESULTS: A single 10-minute dose of 55°C thermal shock reduced bacterial concentrations by 1.47-log CFU/mL, but subsequent incubation allowed bacteria to quickly reach and surpass original starting concentrations. Ciprofloxacin alone achieved a 3.78-log reduction within six hours and prevented significant regrowth during 24 hours of incubation. In combination, thermal shock and antibiotic achieved a 6.20-log reduction within 24 hours. After 24 hours allowing for regrowth, combination therapy produced superior bactericidal effect when compared to antibiotic or heat shock alone. When multiple doses of heat were applied in conjunction with antibiotic exposure, a step-down effect over time was observed as the log reduction achieved by each successive heat shock was either preserved or accentuated by the simultaneous inhibitory activity of the antibiotic. CONCLUSION: The results of this study demonstrate that the bactericidal effects of thermal shock are enhanced by the addition of antibiotics, and appear to show a promising synergistic benefit over either treatment being used alone. Future steps will focus on applying combination therapy to biofilm in an AMF coil in order to determine how dose requirements may differ.