The Interplay of Dispersion and Thermal Shock in Pseudomonas Aeruginosa Biofilms

Pathological bacterial biofilms formed on medical implants pose a significant challenge in clinical settings due to their resistance to antibiotics and the host immune response. Eradication of these biofilms by thermal shock has gained increasing attention as a means of eliminating these infections. The efficacy of such surface-based treatments may be compromised, however, by transient dispersion of bacteria from the biofilm to safer domains, only for them to return to the biofilm after treatment. This study investigates this hypothesis and characterizes this dispersion in closed liquid systems and flow cells to demonstrate a rapid interchange of bacteria between the dispersed and biofilm phases, a preference for bacteria to recolonize established biofilm rather than a bare surface, and the persistence of a sub-population that resists spontaneous dispersion. Studies using layered tissue phantoms estimated an effective dispersion coefficient for dispersed Pseudomonas aeruginosa bacteria of 2 × 10^-10 m²/s, reflecting active transport which ceases after a few minutes at ambient temperature but persists for hours at physiological temperature and is enhanced by thermal shock. Tobramycin, while effective at eliminating planktonic cultures, did not affect the biofilm population or its susceptibility to thermal shock. It did strongly reduce the penetration of dispersed bacteria into the tissue phantom. Replacing the biofilm and substrate with a sterile surface resulted in re-establishment of a new biofilm within 24 h, even in the presence of antibiotics, unless the nearest 2 mm of phantom was also removed, demonstrating the necessity of losing adjacent tissue unless a dispersed-phase treatment operating on the same time scale as the site-specific treatment can be realized.