Acoustically stressing biofilms formed by Pseudomonas aeruginosa

Abstract

Bacterial biofilms, the complex and dynamic assemblages of bacterial cells, have shown increased tolerance to antimicrobials compared to their planktonic counterparts. Altered metabolism and micro-environments, in addition to the self-generated extracellular polymeric substances (EPS), collectively help to protect the bacteria from the effect of antimicrobials, thereby increasing the necessity for novel treatment methods that are effective against biofilms. To address this, we have investigated the effect of high intensity focused ultrasound (HIFU) in killing or dispersing biofilms. HIFU reduces the total biofilm biomass without significant cell killing. To investigate the molecular mechanism of action of HIFU, we quantified the intracellular concentrations of cyclic di-GMP, which regulates the switch between biofilm and planktonic life-styles. Biofilms grown on polymeric sheets were exposed to HIFU at 0.5 MHz frequency and the c di-GMP concentration was characterized using confocal microscopy. Changes in the c di-GMP activity localized at the acoustic focus were observed as the biomass decreased. The mechanisms promoting these changes were further investigated by examining the shape of individual bacterial colony grown on agar plates. The observed effects were compared to sham (negative control) and c di-GMP overproducing mutant (positive control).