Making a surprising discovery, researchers at Worcester Polytechnic Institute (WPI) have found that cranberry juice cocktail blocked a strain of Staphylococcus aureus (S. aureus) from beginning the process of infection.
The WPI researchers were expanding the scope of previous pioneering work on the mechanisms of bacterial infection.
"Most of our work with cranberry juice has been with E. coli and urinary tract infections, but we included Staphylococcus aureus in this study because it is a very serious health threat. This is early data, but the results are surprising," said Terri Camesano, professor of chemical engineering at WPI.
The virulent form of E. coli that Camesano studies is the primary cause of most urinary tract infections.
Strains of S. aureus can cause a range of "staph infections" from minor skin rashes to serious bloodstream infections.
One particular strain, known as Methicillin-resistant Staphylococcus aureus, or MRSA, is a growing public health problem in hospitals, nursing homes, and other institutions because it doesn't respond to most antibiotics.
To cause an infection, bacteria must first adhere to a host, then gather together in colonies to form a biofilm.
In the current study, Camesano recruited healthy female students at WPI to drink either cranberry juice cocktail or a placebo fluid that looked and tasted like cranberry juice.
The subjects provides urine samples at prescribed intervals after drinking the juice or placebo, and those samples were incubated in petri dishes with several strains of E. coli and a single strain of S. aureus. Camesano's team stained the bacteria with a special dye, then used a spectrophotometer to measure the density of the bacterial colonies in the dishes over time.
Their analysis showed that the urine samples from subjects who had recently consumed cranberry juice cocktail significantly reduced the ability of E. coli and S. aureus to form biofilms on the surface of the dishes.
"What was surprising is that Staphylococcus aureus showed the most significant results in this study. We saw essentially no biofilm in the staph samples, which is very surprising because Staph aureus is usually very good at forming biofilms. That's what makes it such a health problem," said Camesano.
The study was reported in a poster presentation at the American Chemical Society's national meeting in Boston.