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To the Editor: Several articles on the clinical utility of cranberry juice in patients with recurrent urinary tract infections have been published.^1-3 Older studies attributed antibacterial activity to organic acids such as hippuric acid.⁴ However, more recent studies have emphasized the role of components that act by interference with bacterial adherence of Escherichia coli.⁵ Thus, it seemed important to reassess whether cranberry juice has true broad-spectrum direct antibacterial activity.

Methods
We tested a 5-fold concentrated preparation of the juice to simulate the cranberry concentrate currently available commercially. The concentrate was diluted 1:1 with trypticase soy broth and adjusted to a pH of 7.0 to ensure that the results would not be confounded by the acidity of the medium. We added an inoculum of approximately 104 colony-forming units per milliliter from an overnight culture of a variety of American Type Culture Collection–quality control strains both to plain broth and the broth to which the cranberry juice had been added. Both cultures were incubated at 35°C and bacterial counts performed in duplicate at 90 minutes and 24 hours.

Results
Table 1 summarizes our results. Using the strain of Klebsiella pneumoniae as an indicator, we also found antibacterial activity in cranberry juice diluted at least as much as 1:32.

View this table: [in this window] [in a new window] Table. Bactericidal Activity of Cranberry Juice Concentrate*

Comment
These preliminary data suggest that concentrated cranberry juice has some antibacterial activity. Although we are now studying the active ingredients, it remains to be seen whether sufficient urinary concentrations of these substances can be achieved.

Yee-Lean Lee, PhD; John Owens, BS; Lauri Thrupp, MD; Thomas C. Cesario, MD
University of California, Irvine

1. Kuzminski LN. Cranberry juice and urinary tract infections: is there a beneficial relationship? Nutr Rev. 1996;54(11 pt 2):S87-S90. 2. Avorn J, Monane M, Gurwitz JH, Glynn RJ, Choodnovskiy I, Lipsitz LA. Reduction of bacteriuria and pyuria after ingestion of cranberry juice. JAMA. 1994;271:751-754. ABSTRACT 3. Walker EB, Barney DP, Mickelsen JN, Walton RJ, Mickelsen RA Jr. Cranberry concentrate: UTI prophylaxis. J Fam Pract. 1997;45:167-168. ISI | PUBMED 4. Bodel PT, Cotran R, Kass EH. Cranberry juice and the antimicrobial action of hippuric acid. J Lab Clin Med. 1959;54:881-888. PUBMED 5. Ofek I, Goldhar J, Zafriri D, Lis H, Adar R, Sharon N. Anti–Escherichia coli adhesion activity of cranberry and blueberry juices [letter]. N Engl J Med. 1991;324:1599. ISI | PUBMED

Letters Section Editors: Phil B. Fontanarosa, MD, Deputy Editor; Stephen J. Lurie, MD, PhD, Fishbein Fellow.

JAMA. 2000;283:1691.

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