Screening of Escherichia coli species biodiversity reveals new biofilm-associated antiadhesion polysaccharides

Abstract

Bacterial biofilms often form multispecies communities in which complex but ill-understood competition and coop-eration interactions occur. In light of the profound physiological modifications associated with this lifestyle, we hypothesizedthat the biofilm environment might represent an untapped source of natural bioactive molecules interfering with bacterial adhe-sion or biofilm formation. We produced cell-free solutions extracted fromin vitromature biofilms formed by 122 naturalEsche-richia coliisolates, and we screened these biofilm extracts for antiadhesion molecules active on a panel of Gram-positive andGram-negative bacteria. Using this approach, we showed that 20% of the tested biofilm extracts contained molecules that antag-onize bacterial growth or adhesion. We characterized a compound, produced by a commensal animalE. colistrain, for whichactivity is detected only in biofilm extract. Biochemical and genetic analyses showed that this compound corresponds to a newtype of released high-molecular-weight polysaccharide whose biofilm-associated production is regulated by the RfaH protein.We demonstrated that the antiadhesion activity of this polysaccharide was restricted to Gram-positive bacteria and that its pro-duction reduced susceptibility to invasion and provided rapid exclusion ofStaphylococcus aureusfrom mixedE. coliandS. au-reusbiofilms. Our results therefore demonstrate that biofilms contain molecules that contribute to the dynamics of mixed bacte-rial communities and that are not or only poorly detected in unconcentrated planktonic supernatants. Systematic identificationof these compounds could lead to strategies that limit pathogen surface colonization and reduce the burden associated with thedevelopment of bacterial biofilms on medical devices.