Implanted medical devices sometimes become infected, resulting in patient suffering and additional surgery for removal or replacement of the device. Implant related infections can usually be controlled with antibiotic therapy, but the infection can rarely be completely eliminated. Once the antibiotic therapy is stopped, the infection returns. The infectious organisms usually exude a polysaccharide slime that appears to protect the bacteria from antibiotic therapy and from the body's defense mechanisms. There are several hypotheses concerning the recalcitrance of the infection toward antibiotic therapy, most of which implicate the exopolysaccharide in reducing the transport of antibiotics or nutrients to the bacteria. The proposed research is centered on eliminating bacterial infections on implant devices using high frequency pressure waves (ultrasound) to work synergistically with antibiotics to kill bacterial biofilms on implant devices. Our preliminary results indicate that ultrasound can enhance transport of antibiotic to cells within the biofilm, and can enhance the action of antibiotics against both sessile and planktonic bacteria. For example, preliminary results show simultaneous application of gentamicin and 2.25 MHz ultrasound to P. aeruginosa biofilms reduces the number of viable cells in the biofilm by 3 orders of magnitude, and that 67 kHz ultrasound reduces viability of sessile and planktonic P. aeruginosa by nearly 3 orders of magnitude. This same level of ultrasonic stimulation has no effect on viability when no antibiotic is present. The effect is also observed with E. coil, and S. fecaelis, The specific aims of this proposal are designed to expand this synergistic effect of ultrasound and antibiotics to increase the killing of biofilms on solid surfaces, and to investigate the underlying physical and chemical mechanisms. 1.1 The project will expose a bacterial biofilm to antibiotics and ultrasound to determine if bacteria are killed beyond that accomplished by the antibiotics alone. Biofilms of P. aeruginosa, S. fecaelis, and E. coil will be tested on polyethylene, polyurethane, silicone rubber, and glass surfaces. 1.2 We have already demonstrated synergistic effects in killing P. aeruginosa and E. coli with gentamicin in combination with 2.25 MHz and 67 kHz ultrasound. We will try to optimize the killing by exploring other frequencies up to 10 MHz, various waveforms, power densities, and the use of another antibiotic. 1.3 We will identify the extent to which ultrasound enhances transport of antibiotic into a bacterium by using ESR spin-labeled antibiotics to measure the kinetics of uptake into bacteria with and without ultrasonic stimulation. This will demonstrate whether the membrane transport is perturbed by ultrasound. 1.4 We will identify the extent to which ultrasound enhances transport within a bacterial biofilm by measuring ultrasonic effects upon transport of antibiotics, oxygen and other molecules through the biofilm.
