The aim of our study was to investigate the bactericidal and bacteriostatic effects of cranberry derived proanthocyanidins (PAC) on Uropathogenic E.Coli (UPEC) in an in vitro environment.

Urinary tract infections (UTIs) are highly prevalent, lead to considerable patient morbidity, incur large financial costs to health-care systems, and are one of the most common reasons for antibiotic use worldwide. The lifetime risk for a woman to develop a UTI is estimated to be over 50% with an additional 25% risk of having a repeat infection in the following 3 - 6 months. UPEC is known to be the culprit in 90% of UTIs. Treatment for UTIs primarily centers on oral antibiotics, which target uropathogens. The armamentarium of effective antibiotics is rapidly diminishing due to increasing resistance, especially in patients afflicted with recurrent UTIs (≥ 3 culture proven episodes per year or ≥ 2 culture proven episodes in 6 months). It is imperative to pursue alternative treatments and prevention methods in patients with acute and recurrent UTIs. Cranberry (Vaccinium macrocarpon) derived proanthocyanidins (PAC) have efficacy in reducing recurrent UTI episodes in patients who are diagnosed with recurrent UTIs. PAC present in cranberries inhibit the binding of P-fimbriae of UPEC to uroepithelial cells. To our knowledge, bactericidal properties of PAC have not been described.

To examine bacterial growth in the presence of PAC, UPEC were grown in liquid luria broth (LB) medium supplemented with 9, 18, or 36 mg of cranberry derived PAC per cm3 of medium. Bacterial growth was determined by plating 50 µl of each culture at 1, 3, 6, 9, and 12 h after incubation in a shaking incubator at 1.5 rotations per minute at 37 °C. A control inoculation of UPEC was grown without treatment in the same environment and plated at each time point. The plates were observed for 48 h and the number of colonies were counted at 12, 24, and 48 h using ImageJ2 software.

All PAC treated inoculations (9, 18, and 36 mg/cm3) incubated for 3h or greater had no colony growth at each measured time point (Fig 1), suggesting a bactericidal effect. In comparison, growth in control plates for 3, 6, 9, and 12 h incubation time points filled ≥ 88% of the plate at 24 h. Of PAC treated inoculations incubated for 1h, the 18 and 36 mg/cm3 had 0 colonies at all measured time points. We show that the 9 mg/cm3 PAC (1 h incubation) had a delayed growth, suggesting a bacteriostatic effect, compared to the untreated control. There also were fewer colonies (Fig 2A), and smaller coverage areas (Fig 2B) at all time points.

Our data suggest that cranberry derived PAC may have a bactericidal effect on UPEC. The effect of PAC on UPEC may be dependent on dose and incubation time. Additionally, our data add to existing literature describing inhibition of UPEC when treated with cranberry derived PAC.

Experiments to establish safety profiles and in vivo effects will need to be performed in animal models. If cranberry derived PAC are deemed to be safe and efficacious for the treatment of UPEC, the substance could have a tremendous effect against the antibiotic resistance crisis.