315 - Alternating Magnetic Fields (AMF) and Antibiotics Eradicate Biofilm on Metal in a Synergistic Fashion

Background: Hundreds of thousands of human implant procedures require surgical revision each year due to infection. Implant infections are difficult to treat with conventional antibiotics due to the formation of biofilm on the device surface. We have developed a non-invasive method to treat metal implant infections using alternating magnetic fields (AMF). The outer surface of a metal implant is heated when exposed to AMF, and we hypothesize that this heating can be used to eradicate biofilm or sensitize them to antibiotics (Fig 1). This study investigated the interaction of biofilm and antibiotics in vitro.Fig 1. Scheme showing the principle of AMF treating metal implant infection (MII).


Methods: P. aeruginosa (PAO1) and Staphylococcus aureus (UAMS1) biofilms were cultured on stainless steel rings. The biofilms were then treated as in Fig 2, receiving a series of AMF exposures every 12 hours. Each dose of AMF was comprised of multiple 3s-AMF exposures every 5 min, with a peak ring temperature of 65 °C. Biofilms were incubated in the presence or absence 0.5 mg/mL ciprofloxacin or ceftriaxone. At the end of 12 and 24 hours, samples were harvested and colony forming units (CFU) were calculated.Fig 2. AMF treatment design.


Results: AMF alone resulted in a transient decrease in CFU which recovered by the second dose. Antibiotics alone resulted in an ~2-log decrease in CFU at 24 hours. However, the combination of AMF plus cipro showed a synergistic response with a >4-log decrease (Fig 3a). Confocal microscopy confirmed these findings. This effect was not limited to Pseudomonas aeruginosa as similar synergistic responses were seen with Staphylococcus aureus and ceftriaxone (Fig 3b).Fig 3 The bacteria number (CFU) change during 24 hr AMF and antibiotics treatment session. a) P. aeruginosa (PAO1) treated with AMF and ciprofloxacin. b) Staphylococcus aureus (UAMS1) treated with AMF and ceftriaxone.


Conclusion: When combined with antibiotics, AMF displays a synergistic effect in eradicating biofilm. This effect was seen in different pathogens and in multiple antibiotics. Synergy was seen at different target temperatures as well. This interaction has important implications for deployment of this innovative non-invasive approach to treating biofilm-related infections on metal implants.