Fighting bacterial infection with… cranberries?


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It seems like every couple of weeks, there is a recall on another food product for possible E. coli contamination.

Although Escherichia coli bacteria normally live in the intestines of people and animals, some strains can cause illness. The types of E. coli that can cause diarrhea, explains the Centers for Disease Control and Prevention (CDC) can be transmitted through contaminated water or food or through contact with animals or people.

According to the CDC, there are six pathotypes are associated with diarrhea:

  • Shiga toxin-producing E. coli (STEC) — STEC may also be referred to as Verocytotoxin-producing E. coli (VTEC) or enterohemorrhagic E. coli (EHEC). This pathotype is the one most commonly heard about in the news in association with food-borne outbreaks.
  • Enterotoxigenic E. coli (ETEC)
  • Enteropathogenic E. coli (EPEC)
  • Enteroaggregative E. coli (EAEC)
  • Enteroinvasive E. coli (EIEC)
  • Diffusely adherent E. coli (DAEC)

The bacterial infection is increasingly worrying, not only because of the number of outbreaks we've had this year alone, but also because of the rise of superbugs that are resistant to current antibiotics.

Researchers at Worcester Polytechnic Institute and the University of Massachusetts Dartmouth wanted a better understanding of the mechanisms of bacterial infection so they can identify potential new antibiotic drug targets. They found a potential solution in the additional compounds of cranberry juice.


Tackling bacterial infections with cranberriesBlocking bacteria with cranberries

The research team characterized the role of compounds in cranberry juice that block the critical first step in bacterial infections. The results open a potential new area of focus for antibiotic drug development.

Led by Terri Camesano, PhD, professor of chemical engineering and dean of graduate studies at WPI, and Catherine Neto, PhD, professor and chair of chemistry and biochemistry at UMass Dartmouth, the team reported its findings in the paper "Atomic force microscopy-guided fractionation reveals the influence of cranberry phytochemicals on adhesion of Escherichia coli" published in the Royal Society of Chemistry journal Food & Function.

According to the CDC, at least 2 million Americans are infected each year with drug-resistant bacteria, while some 23,000 die from those infections. To cause an infection, bacteria must first adhere to a host and accumulate in sufficient numbers to form a biofilm.

In the new paper, the team reports that compounds in cranberry juice called flavonols greatly reduced the ability of the bacteria E. coli to stick to a surface (various strains of E. coli are responsible for many types of infections, including those of the urinary tract).

Previous work by Camesano, Neto and others has shown that a group of compounds called proanthocyanidins (PACs) likely play a role in cranberry juice's ability to block bacterial adhesion.

In the new study, Neto's team used advanced chemical techniques to separate or "fractionate" cranberry juice into its constituent chemical compounds and characterize them. Then at WPI, Camesano's team cultured E. coli cells in samples of the fractionated juice and used an atomic force microscope to measure the bacteria's ability to bond to a surface.

"This study is the first to combine an assay-guided fractionation approach with atomic force microscopy to identify cranberry juice constituents that most strongly influence E. coli adhesion forces," the authors wrote.


Refreshing results

After the first round of testing, samples that showed the greatest ability to reduce E. coli adhesion were further fractionated at UMass Dartmouth and then returned to WPI for testing. The process went on in similar cycles, further reducing the number of compounds in each sample, to home in on the key chemicals affecting adhesion.

Those tests found that flavonols significantly reduced E. coli adhesion, both on their own, and in the presence of PACs. One particular group called flavonol galactosides showed the strongest results. "Like the PACs, we think the flavonols are part of the plant's defense system," Neto said. "They are secondary metabolites that are produced in greater concentrations when the plant is under stress or in the presence of pathogens."

The new data builds on previously published work, in which Camesano and her team showed that cranberry juice compresses the tiny tendrils (known as fimbriae) on the surface of the E. coli bacteria that enable it to bind tightly to the lining of the urinary tract.

The change in shape greatly reduces the ability of the bacteria to stay put long enough to initiate an infection. Flavonols also are likely to affect the ability of fimbriae to bind to surfaces, but in a different way than PACs do, Camesano noted.

"This strongly suggests the anti-adhesive role of other classes of cranberry compounds in conjunction with already known PACs and may have implications for development of alternative antibacterial treatments," the authors wrote. "These compounds should be further explored, both individually and in combination for their antimicrobial properties against various bacterial diseases [to] give us a therapeutic edge against these 'superbugs.'"

For more information about superbugs that are resistant to current antibiotic treatments, see the CDC resource page.