Bacterial biofilm shows persistent resistance to liquid wetting and gas penetration

• DOI: 10.1073/pnas.1011033108
• Publication Date: 2010-12-30T10:15:48Z
• Authors: Alexander K. Epstein; Boaz Pokroy; Agnese Seminara; Joanna Aizenberg
• Keywords: 0301 basic medicine; microcomputed tomography; Microscopy, Confocal; Ethanol; Chemistry, Physical; Surface Properties; Antimicrobial resistance; Biofilm hydrophobicity; Liquid repellency; Microcomputed tomography; Nonwettability; Bacillus subtilis; Chemistry, Physical; Disinfectants; Ethanol; Extracellular Matrix; Microscopy, Confocal; Solvents; Surface Properties; X-Ray Microtomography; Biofilms; Wettability; X-Ray Microtomography; 620; Extracellular Matrix; biofilm hydrophobicity; nonwettability; 03 medical and health sciences; liquid repellency; Biofilms; Solvents; Wettability; antimicrobial resistance; Bacillus subtilis; Disinfectants

Most of the world’s bacteria exist in robust, sessile communities known as biofilms, ubiquitously adherent to environmental surfaces from ocean floors to human teeth and notoriously resistant to antimicrobial agents. We report the surprising observation that Bacillus subtilis biofilm colonies and pellicles are extremely nonwetting, greatly surpassing the repellency of Teflon toward water and lower surface tension liquids. The biofilm surface remains nonwetting against up to 80% ethanol as well as other organic solvents and commercial biocides across a large and clinically important concentration range. We show that this property limits the penetration of antimicrobial liquids into the biofilm, severely compromising their efficacy. To highlight the mechanisms of this phenomenon, we performed experiments with mutant biofilms lacking ECM components and with functionalized polymeric replicas of biofilm microstructure. We show that the nonwetting properties are a synergistic result of ECM composition, multiscale roughness, reentrant topography, and possibly yet other factors related to the dynamic nature of the biofilm surface. Finally, we report the impenetrability of the biofilm surface by gases, implying defense capability against vapor-phase antimicrobials as well. These remarkable properties of B. subtilis biofilm, which may have evolved as a protection mechanism against native environmental threats, provide a new direction in both antimicrobial research and bioinspired liquid-repellent surface paradigms.