Bacterial Anti-adhesion Activity of Cranberry Proanthocyanidins

Amy Howell, Ph.D.
Marucci Center for Blueberry Cranberry Research
Rutgers University, Chatsworth, NJ

The American Cranberry (Vaccinium macrocarpon Ait) has been utilized medicinally for hundreds of years, and more recently has demonstrated a broad array of health benefits in a number of research studies.  Consumption of cranberry juice has been associated with prevention of urinary tract infections, and several well-designed clinical studies have confirmed this association (Avorn et al., 1994; Kontiokari et al., 2001).  For years, the preventative effects of cranberry were assumed to be due to the acidity of the fruit; however the majority of clinical studies have demonstrated that a bacteriostatic pH is rarely achieved in urine following normal serving sizes of cranberry (Avorn et al., 1994, Walker et al., 1997). 

Urinary tract infection is initiated by bacterial adherence to the uroepithelium, followed by bacterial multiplication and colonization of the urinary tract (Beachy, 1981).  Cranberries contain a group of polyphenolic compounds called proanthocyanidins (PACs) with double A-type linkages that inhibit P-fimbriated E. coli from adhering to the uroepithelial cells (Howell et al., 1998, Foo et al., 2000a,b), thus preventing growth and subsequent infection.  These PACs are different from those found in other foods, such as chocolate and grape that contain single B-type linkages between flavan-3-ol units (Gu et al., 2003).  Recent studies suggest that cranberry PACs may induce conformational changes in bacteria that influence their adhesion activity (Liu et al., 2006).

Cranberry PACs are associated with preventing bacterial adhesion not only in the urinary tract, but also in the stomach and oral cavity.  They prevented Helicobacter pylori, the bacteria associated with the onset of stomach ulcers, from attaching to isolated stomach cells (Burger et al., 2000). In a randomized placebo-controlled clinical study in China, consumption of two 250-ml servings of cranberry juice cocktail (27% cranberry) per day accounted for a 15% suppression of H. pylori (Zhang et al., 2005).  Cranberry PAC extracts have also demonstrated activity in the oral cavity preventing biofilms associated with coaggregation and adhesion of bacteria to teeth and gums (Weiss et al., 2002), and prevented adhesion of Streptoccocus sobrinus to hydroxyapatite (Steinberg et al., 2004). 

Inhibiting bacterial adhesion to prevent infections rather than prescribing low-dose antibiotics is of interest to many researchers, as the mechanism of anti-adherence does not kill bacteria and lead to significant selection pressure favoring survival of antibiotic resistant bacterial strains (Ofek et al., 2003).  Therefore, utilizing cranberry and/or cranberry PACs to prevent certain bacterial infections could potentially help to slow the pace of antibiotic resistance development. Preventative strategies such as this could become increasingly important as rates of antibiotic resistance continue to increase due to over-use of antibiotics (Gupta et al., 2001).

Keywords: Cranberry, Vaccinium macrocarpon, bacteria, Escherichia coli, adhesion, urinary, ulcer, oral cavity, proanthocyanidin       

References:
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