Thermal shock susceptibility and regrowth of Pseudomonas aeruginosa biofilms

Abstract

Biofilms on implanted medical devices cause thousands of patients each year to undergo multiple surgeries to remove and replace the implant, driving billions of dollars in increased health care costs due to the lack of viable treatment options for in situ biofilm eradication. Remotely activated localised heating is under investigation to mitigate these biofilms; however, little is known about the temperatures required to kill the biofilms. To better understand the required parameters this study investigated the thermal susceptibility of biofilms as a function of their fluidic and chemical environment during growth, as well as their propensity for regrowth following thermal shock. Pseudomonas aeruginosa biofilms were cultured in shaker plate fluidic conditions in four different growth media, then thermally shocked at various temperatures and exposure times. Biofilms were re-incubated to determine their regrowth potential following thermal shocks of various intensities. Results indicate that growth media has little impact on thermal susceptibility, while fluidic conditions strongly influence susceptibility to modest thermal shocks. This effect disappears, however, with increasingly aggressive shocks, reducing biofilm populations by up to 5 orders of magnitude. Regrowth studies indicate a critical post-shock bacterial loading (∼10³ CFU/cm²) below which the biofilms were no longer viable, while biofilms above that loading slowly regrew to their previous population density.

Keywords:

• Heat shock response
• non-oncologic applications of hyperthermia
• bacterial infection

Disclosure statement

The authors declare no financial or commercial competing interests.

Additional information

Funding

This work was supported in part by the American Heart Association (11SDG7600044) and the National Science Foundation (CBET-1133297). E. Ricker was supported by the Predoctoral Training Program in Biotechnology from the National Institute for General Medical Sciences of the National Institutes of Health (T32 GM008365). The Zeiss LSM 710 confocal microscope was also obtained with support from the National Institutes of Health (1 S10 RR025439–01). The content of this material is solely the responsibility of the authors and does not necessarily represent the official views of the supporting agencies.