The Polymeric Matrix Composition of Biofilms Modulate Resistance to Silver Nanoparticles Prepared by Hydrothermal Synthesis.

Biofilms represent the dominant microbial lifestyle in nature. These complex microbial communities in which bacteria are embedded in a self-produced protective polymeric extracellular matrix, display an enhanced resistance to antimicrobials and thus represent a major health challenge. Although nanoparticles have proven to be effective against bacteria, the interactions between nanoparticles and the polymeric biofilm matrix are still unclear. In this work, silver nanoparticles (AgNPs) were used on mature biofilms formed by the pathogen , and their effects on the biofilm microstructure were evaluated. Bacteria cells within mature biofilms showed an increased tolerance to AgNPs, with their elimination requiring a concentration nine times higher than planktonic cells. Mutant strains not able to form a pellicle biofilm were four times more susceptible to AgNPs than the wild-type strain forming a strong biofilm. Moreover, electron microscopy analysis revealed that AgNPs interacted with the extracellular matrix components and disrupted its microstructure. Finally, two major proteins, Bap1 and RbmA, appeared to mediate the biofilm bacterial resistance to AgNPs. This work highlights the role of the polymeric biofilm matrix composition in resistance to AgNPs. It underlines how crucial it is to understand and characterize the interactions between nanoparticles and the biofilm matrix, in order to design appropriate metallic nanoparticles efficient against bacterial biofilms.