Mechanisms for Reducing UTI

Bacteria can be killed in a number of ways: extremes of temperature, radiation, electrical currents, extremes of pH, and numerous antimicrobial compounds. Obviously the first three options are not possible within a patient, but most fruit juices have a low pH (high acidity). Many juices also contain organic acids and other compounds that naturally inhibit bacteria. Escherichia coli are gram-positive bacteria naturally present in the large intestine, but they may contaminate the urinary tract. E. coli have pili or fimbriae on their surface that resemble hairs. These fimbriae contain two types of adhesins, compounds that promote adhesion to other cells, such as the epithelial cells lining the bladder. One adhesin is called mannose-specific (MS) since it preferentially binds to the sugar mannose. Fructose is the only other sugar that can bind to this adhesin. Most E. coli strains from urinary tract infections have Type I fimbriae that have this MS adhesin.

The other adhesin is referred to as mannose-resistant (MR), since it does not bind to either sugar. MR adhesin is found in E. coli strains from both diarrhea and urinary tract infections. This adhesin appears to be inhibited by large-molecular weight compounds that are not yet clearly identified (Ofek et al., 1996). Binding these inhibitors prevents the bacteria from attaching to other cells, thus producing an inhibitory effect on their infective ability.

Blueberries and cranberries appear to have unique phytochemical mixtures that aid in reduction of urinary tract pathogens. The combination of low pH, organic acids, fructose, and MR-adhesin inhibitors provide a hurdle effect (Figure 3.4). By using several methods to kill bacteria, or in the case of UTIs, preventing adhesion of bacteria to tissues, bacterial strains resistant to one process will be overcome by another, resulting in a minimal microbial risk.

Ascorbic acid

Ascorbic acid

Direct antimicrobial agents

Compounds that interfere with binding of fimbrae

Fructose

Direct antimicrobial agents

Compounds that interfere with binding of fimbrae

Organic acids

Proanthocyanidins

Figure 3.4 Possible mechanisms for antimicrobial activity of Vaccinium phytochemicals.

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