(222f) Dynamics of Biofilm Elimination on Thermally Shocked Biomedical Surfaces

When bacteria colonize a medical implant surface, they form a biofilm which cannot be eradicated chemically. The current standard of care is surgical explantation of the device and surrounding tissue, with eventual reimplantation of a replacement device with twice the probability of infection. These infections are a $5 billion problem in the U.S. alone, impacting over 100,000 patients annually. One approach to mitigating these biofilms is in situ thermal eradication by generating a thermal shock directly at the device/biofilm interface. We have developed magnetic nanoparticle / polymer composite coatings which heat rapidly when exposed to an externally applied alternating magnetic field, and have quantified immediate bacterial population reductions of up to 6 orders of magnitude (i.e., “6-log” reductions).

Moreover, under certain circumstances the biofilm bacterial population continues to decrease for hours after the thermal shock is removed and physiological temperature is restored, resulting in complete eradication of the biofilm. Re-incubation studies at a variety of shock temperatures (50 – 80 °C) and exposure times (1 – 30 min) showed that thermal shocks producing immediate population reductions greater than 4-log resulted in complete elimination of the biofilm approximately 4 hours later, regardless of the temperature/exposure time combination used to achieve the immediate reduction. Biofilms subjected to thermal shocks with more modest immediate population reductions (less than 4-log) grew back to their initial population density within 24 hours. These investigations were extended to biofilms with different culture conditions producing pre-shock population densities 100 times greater than the earlier biofilms (nearly 10⁹ CFU/cm²). Despite the substantially larger initial population density, the same immediate population reduction (4-log) was required to prompt eventual die-off of the biofilm, even though the population density immediately after the thermal shock was 100 times greater than in the previous studies. This suggests that the degree of thermal shock required to eradicate a biofilm is independent of the biofilm’s initial population density.

Furthermore, this approach may be integrated with other modifications to the biofilm/device interface to prevent or eliminate biofilms with even milder thermal shocks. Investigations of combined thermal shock and antibiotic exposure yielded population reductions whose orders of magnitude were greater than the sum of the orders of magnitude reduction for either treatment alone, enabling significantly milder thermal shocks to provide the same efficacy and providing an impetus for localized delivery at the device interface of antibiotics which are by themselves insufficient for biofilm elimination.