BACKGROUND: The inhibition of Escherichia coli growth in the presence of Vaccinium macrocarpon has been extensively described; however, the mechanisms of this activity are not well characterized.

FINDINGS: Here, E. coli was grown in media spiked with cranberry juice. The growth rate and media pH were monitored over more than 300 generations. The pH of the growth media was found to decrease during cell growth. This result was unique to media spiked with cranberry juice and was not reproduced through the addition of sugars, proanthocyanidins, or metal chelators to growth media.

CONCLUSION: This study demonstrated that factors other than sugars or proanthocyanidins in cranberry juice result in acidification of the growth media. Further studies are necessary for a complete understanding of the antimicrobial activity of cranberry products.