Those soda fountain machines found in restaurants and fast food joints may be squirting out liquids contaminated with fecal bacteria, a small study found.
Whether it was self-serve or behind the counter, nearly half of all sodas dispensed from a sample of 30 machines in the Roanoke Valley in Virginia had coliform bacteria -- a group of bacteria banned in drinking water by the U.S. Environmental Protection Agency (EPA) because it indicates the possibility of fecal contamination.
"The EPA regulates our drinking supply, and there can be some bacteria, but one of the things that is not allowed is coliform bacteria," said Renee D. Godard, professor of biology at Hollins University and a co-author of the paper published in the January print issue of the International Journal of Food Microbiology.
"We can't have that in our drinking supply. But they're coming out of these soda fountain machines," she said.
The soda machines had turned into a bacteria metropolis with Escherichia coli (E. coli), species of Klebsiella, Staphylococcus, Stenotrophomonas, Candida, and Serratia. Most of the bacteria were resistant to the 11 antibiotics Godard tested on her samples.
"About 70 percent of the beverages had bacteria and 48 percent of them had coliform bacteria," said Godard.
However, only 20 percent of the sodas sampled had coliform bacteria that exceeded the EPA limit for drinking water.
Since the tap water and ice from the machines didn't test positive for bacteria, Godard and her team ruled out the possibility of a valley-wide contamination of the water supply.
Various brands of soft drinks and various types -- sugared, diet or even water -- were contaminated, leading Godard to think that it wasn't the soda, but the machine that was growing bacteria.
From all her testing, Godard still isn't sure where the bacteria came from. Few people observed in the restaurants touched the nozzles of the soda fountain machines and restaurant managers Godard interviewed reported cleaning the nozzles daily.
But only one restaurant manager reported rinsing the plastic tubing within the machines on a regular basis.
Godard hypothesizes that it could only take one contamination of the nozzle for the bacteria to grow up into the plastic tubing and start colonizing within the machine.
"Our best guess is they're actually establishing themselves on the lining of the plastic tubing. The reason we say that is in other areas, such as hospitals, it is known that bacteria can establish themselves on plastic tubing for machines," said Godard.
The Coca-Cola Company, said in a statement to ABCNews.com that it "has been serving fountain beverages for more than 120 years, and we are not aware of any illnesses related to our fountain-dispensed beverages and the microorganisms mentioned in the Virginia study."
Coca-Cola said it purchases the soda fountain dispensers from independent companies and "routinely communicate with our customers, who maintain the fountain equipment, about our standards and expectations for quality and sanitation, and we provide them with training," according to the company's statements.
Godard said she hopes the news will lead restaurant owners to rinse out their machines more often.