(210c) Thermal Shock Dynamics on Biofilm Viability at Biomedical Interfaces

Authors: 
Aljaafari, H., University of Iowa
Nuxoll, E., University of Iowa
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 a critical drop resulted in complete elimination of the biofilm several hours later.

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 orders of magnitude population reductions 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.

These investigations were done on biofilms of two different types of bacteria (Pseudomonas aeruginosa and Staphylococcus aureus), which were both cultured using two different protocols (shaker table and drip flow reactor). Despite the type of bacteria or the substantially larger difference in the initial population density due to the culturing protocol, an immediate critical population drop was required to prompt eventual die-off of the biofilm. Using antibiotics make this critical drop achievable at milder thermal shock. This suggests that biofilms on medical implant devices can be thermally mitigated at milder thermal shock than previously believed.