[Does cranberry juice have bacteriostatic activity?].

Background: Cranberry juice is used to prevent urinary infections but it is not known if it inhibits bacterial growth in urine or in bacteriologic broth.

Objective: Determining if cranberry juice has bacteriostatic properties.

Methods: The urine of 20 female university students was studied before and after drinking cranberry juice. Both specimens were submitted to pH determination and inoculated with a control strain of Escherichia coli. After 1 and 2 hours of incubation with the inoculum, the urine specimens were plated on agar to determine their bacterial counts. Additionally, the growth of 10 E. coli strains were studied in broths with serial dilutions of juice.

Results: No inhibitory effect on bacterial growth was observed in urine after drinking cranberry juice. After 1 and two hours of incubation with the E. coli inoculum, control urine grew an average 132.2 and 153 x 10(3) colony-forming units/mL, respectively. After 1 and two hours of incubation with the inoculum, post-intervention urine grew an average 141.4 and 170.6 x 10(3) CFU/mL, respectively (p > 0.05). Against expectations, an increment was observed in urinary pH after drinking the juice (average pH in controls, 5.8 vs. 6.2 in post-intervention specimens; p = 0.043). In vitro analysis did not find a negative trend of E. coli growth in broths with higher concentrations of juice.

Conclusions: Cranberry juice was not associated with bacteriostatic properties and its ingestion was not followed by a drop in urinary pH, which suggests that these are not its potential beneficial effects for the management and the prevention of urinary tract infections.