The researchers, led by Dr Terri Camesano, professor of chemical engineering at Worcester Polytechnic Institute (WPI), reported the surprise finding of the study - that that a cranberry juice cocktail blocked a strain of Staphylococcus aureus (S. aureus) from beginning the process of 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," Prof Camesano said. "This is early data, but the results are surprising."
Cranberry has long been linked with protection from UTIs, with previous studies showing mixed reviews for the benefits of cranberry juice.
In a systematic review of the evidence the Cochrane collaboration reported: “There is some evidence that cranberry juice may decrease the number of symptomatic UTIs over a 12 month period, particularly for women with recurrent UTIs.”
However, last year the European Food Safety Authority (EFSA) issued a negative opinion to global cranberry leader Ocean Spray for an article 14 health claim relating consumption of cranberry and urinary tract infection (UTI) in women.
E. coli is accountable for around 80 percent of urinary tract infections (UTIs), whilst S. aureus can cause a range of "staph infections", ranging from minor skin rashes to serious infections like toxic shock syndrome.
Antibiotic resistant strains of S. aureus like Methicillin-resistant Staphylococcus aureus (MRSA) are a growing problem – in the USA deaths from MRSA more than doubled between 199 and 2005.
Infection occurs when bacteria manage to adhere to a host cell and form a biofilm, this thin film creates an environment where the bacteria can multiply and thrive.
The researchers tested a cranberry juice cocktail against placebo fluid that looked and tasted like cranberry juice. Urine samples were then incubated in petri dishes with strains of E. coli or S. aureus.
Analysis showed 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,” said Camesano.
"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,” she added.
In E. coli it is known that small hair-like projections known as fimbriae act like hooks and help the bacteria attach to cells lining the urinary tract.
Exposure to cranberry juice is suggested to cause the fimbriae on E. coli to curl up, blunting their ability to attach to cells, so offering a possible protective effect for UTIs.
Howver, S. aureus do not have fimbirae like E. coli.
“There must be other reasons why the cranberry juice affected its biofilm formation in the study,” suggests Prof Camesano.
The results of the research have been said to “create more questions than answers."
"We believe this is an important new area to explore, and we are now thinking about how best to proceed," added Camesano.
Source: Data was reported by Dr Terri Camesano in a poster presentation at the national meeting for the American Chemical Society, in Boston, August 23 2010.