Media acidification by Escherichia coli in the presence of cranberry juice

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.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.Early studies focusing on the antimicrobial activity of Vaccinium macrocarpon (cranberry) implicated the acidifying effect the juice had on urine and/or increased excretion of the cranberry metabolite hippuric acid as potential antimicrobial mechanisms [1-3]. Studies demonstrated that consumption of cranberry juice did lower urinary pH, however, no direct bacteriostatic effect was observed from the urine samples [2,3]. Other studies have reported no change in urinary pH upon consumption of cranberry juice [4,5]. More recently, the evidence for the role of urinary acidification by cranberry juice has been called into question [5-7]. Rhee suggests that ascorbic acid in the cranberry juice may facilitate non-enzymatic generation of nitric oxide (NO) which possesses potent antimicrobial activities [7]. The growth of E. coli was markedly inhibited in mildly acidified urine when nitrite was present [8]. Current studies tend to implicate the anti-adhesive properties of the A-type proanthocyanidins (PACs) found in cranberries in the reduction of urinary tract infection as well as in health benefits related to the prevention of oral biofilms and stomach ulcers [6,9-12]. In addition to these mechanisms of action, alterations to the growth rate of bacteria were implicated in contributing to the overall antimicrobial activity observed [13]. Many recent studies ha