Cranberry (Vaccinium macrocarpon) has been reported to inhibit bacterial adhesion, co-aggregation and biofilm formation, and previous studies have shown that several constituents including proanthocyanidins, flavonols and polysaccharides may work synergistically to reduce E. coli adhesion forces and co-aggregation of oral bacteria. Several Enterococcus and Streptococcus strains were selected for further evaluation based on their clinical relevance in prostate infections, dental caries, and throat infections; information on cranberry’s efficacy against these organisms is lacking. Isolates from whole cranberry fruit were evaluated for their biofilm inhibitory capability alone and in combination, using a crystal violet stain biofilm assay. Several fractions inhibited biofilm formation in a dose-dependent manner. A fraction containing primarily A-type proanthocyanidin oligomers ranging from 2 to 7 (epi)catechin units, was a potent inhibitor in all organisms at 62.5 ug/mL. Anthocyanin-containing fractions showed greater selectivity for Enterococcus spp. while fractions containing primarily flavonols were more effective on Streptococcus spp. Evaluation of their synergistic effects is ongoing. Cranberry may help reduce infection by these pathogens by interfering with the initial steps of adhesion and biofilm formation, and are less likely to promote development of antibiotic-resistant strains.

Inhibition of Streptococcus and Enterococcus biofilms by cranberry bioactives

256th National Meeting (2018)

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