Cranberries are a rich source of proanthocyanidins, a type of antioxidant flavonoid, and some previous studies have suggested that the compound lends cranberry juice its infection-fighting properties.  Terri Camesano, from Worcester Polytechnic Institute (Massachusetts, USA), and colleagues have been exploring the mechanisms that the virulent form of E. coli bacteria, the primary cause of most urinary tract infections (UTIs) in people, uses to form biofilms – the precursor to infection. Previously, the team has shown that exposure to cranberry juice causes the hair-like projections on E. coli responsible for initiating the biofilm to curl up, reducing their ability to attach to urinary tract cells. In the new study, the researchers incubated two different strains of E. coli in the presence of two different mixtures of commercially available cranberry juice cocktail. They also incubated the bacteria separately in the presence of proanthocyanidins, but not juice.  The result was that the juice cultures completely prevented biofilm formation, whereas the PACs showed only limited ability to reduce biofilm formation.  The researchers conclude that:  “These results demonstrate that [cranberry juice] is more effective than isolated [proanthocyanidins] at preventing biofilm formation, possibly suggesting that other cranberry compounds also play a role in anti-biofilm activity.”