Alternating magnetic fields and antibiotics eradicate biofilm on metal in a synergistic fashion

Millions of metal implants are used annually, but 2-4% become infected, leading to costly and invasive surgical revisions. The formation of biofilm on the implant surface is a major contributor to treatment failure. Biofilms, composed of bacteria and extracellular polymeric substances (EPS), make bacteria highly resistant to antibiotics and the immune system. Current treatments focus on multiple surgical revisions and prolonged antibiotic administration, often with unsatisfactory results. Non-surgical biofilm eradication methods are urgently needed. Previous studies demonstrated that alternating magnetic fields (AMF) generate heat on metal implants, reducing biofilm. However, maintaining high temperatures for extended periods poses challenges and incomplete eradication can lead to biofilm reformation. This study explored the synergistic effect of combining iAMF with antibiotics, hypothesizing that brief, intermittent iAMF exposures combined with antibiotic treatment would improve efficacy and reduce tissue damage.

The literature review highlights the significant challenge posed by implant-associated infections due to biofilm formation. Existing physical methods like electrical currents, ultrasound, and heat have limitations in application to metal implants. AMF, however, offers a potential advantage due to its non-invasive nature and ability to induce heat on implant surfaces. Prior research showed the feasibility of AMF in biofilm reduction but also noted the limitation of sustained high temperatures and incomplete eradication. The concept of combination therapy with antibiotics is introduced based on previous in vitro studies demonstrating enhanced biofilm reduction with AMF and ciprofloxacin.

The study utilized a custom-designed in vitro system with multiple solenoid coils to generate precisely controlled intermittent alternating magnetic fields (iAMF). Stainless-steel rings were used as models for metal implants. Biofilms of *P. aeruginosa* (PAO1) and *S. aureus* (JA1M5) were grown on these rings. The iAMF system allowed for precise control of parameters such as target temperature (Tmax), exposure duration (tExp), and rest intervals (dRest). Various iAMF settings were investigated, including different Tmax (50°C, 65°C, 80°C), dose durations (15 min to 1 h), and dosing intervals. The effects of iAMF alone, antibiotics alone (ciprofloxacin, linezolid, or ceftriaxone at MICs), and the combination of iAMF and antibiotics were assessed by quantifying colony-forming units (CFU) at various time points (0, 12, and 24 h). A multidrug-resistant (MDR) *P. aeruginosa* strain (MB689) was used to investigate the mechanism of synergy. Laser scanning confocal microscopy and scanning electron microscopy (SEM) were employed to visualize biofilm morphology after treatment. Statistical analysis using two-way ANOVA was performed to compare bacterial burden among different treatment groups.

The iAMF system effectively heated the metal rings with minimal heating of the surrounding media. iAMF alone reduced *P. aeruginosa* biofilm by 1–2 log CFU per dose, but the CFU levels reverted to baseline between doses. Ciprofloxacin alone showed a steady reduction, plateauing after 12 h. The combination of iAMF and ciprofloxacin resulted in a consistent and significant reduction of *P. aeruginosa* biofilm down to the limit of detection. The synergistic effect was dose-dependent, with longer iAMF durations resulting in greater reductions. Similar results were observed with *S. aureus* biofilms treated with iAMF and linezolid or ceftriaxone. The combination therapy was effective across different iAMF settings. Microscopy revealed morphological changes in biofilms after iAMF and antibiotic treatment, suggesting membrane disruption. In the MDR *P. aeruginosa* strain (MB689), iAMF rescued the activity of meropenem, but not ciprofloxacin, suggesting a possible mechanism related to membrane disruption. The combined treatment also proved effective against biofilms of different ages (2-day and 7-day old biofilms). The synergistic effect was not observed on plastic rings, indicating that the interaction between AMF and metal is crucial.

The study successfully demonstrates the synergistic effect of iAMF and antibiotics in eradicating biofilms from metal implant surfaces. The results suggest a mechanism involving membrane disruption by iAMF, which enhances antibiotic penetration and efficacy. The ability to rescue the activity of meropenem in an MDR strain highlights the potential of this approach in combating antibiotic resistance. The non-invasive nature of iAMF offers a significant advantage over current surgical interventions. While the study focuses on in vitro experiments, the findings strongly support the potential of translating this approach to in vivo settings. Further investigation is warranted to optimize treatment parameters and fully elucidate the mechanisms involved.

This study provides strong evidence for the synergistic efficacy of combining intermittent alternating magnetic fields (iAMF) and antibiotics in eradicating biofilms from metal implant surfaces. The findings suggest a novel non-invasive approach to treat implant-associated infections, particularly those caused by multidrug-resistant bacteria. Further research should focus on in vivo studies to validate the findings and optimize treatment parameters for clinical application.

The study was conducted in vitro, limiting the direct applicability to in vivo settings. The complex interplay between iAMF, metal, and antibiotics requires further investigation to completely elucidate the mechanisms involved. The optimal treatment parameters (number of doses, target temperature) for in vivo application remain to be determined. The study focused on specific bacterial strains and antibiotics; further research is needed to assess broader applicability across different pathogens and resistance mechanisms.