You may want to think twice the next time you’re compelled to buy a drink from a soda fountain machine.  According to a study published in the January 2010 issue of the International Journal of Food Microbiology, it may not be safe.

Researchers at Hollins University in Virginia found the presence of coliform bacteria in nearly half of the 90 beverages sampled from soda fountain machines in one area of Virginia.  Most of the machines were located in fast food restaurants and/or convenience stores.

Whether it was self-serve or behind the counter, 48% of beverages from a sample of 30 machines in Roanoke Valley, Virginia tested positive for coliform bacteria. The EPA bans coliform bacteria in drinking water and beverages because it often indicates fecal contamination.

Coliform was not the only strain of bacteria to be isolated – approximately 70% of the beverages tested positive for some kind of bacteria, and more than 11% of the beverages analyzed contained Escherichia coli (E. coli). Several other types of opportunistic bacteria were detected, including Staphylococcus (Staph). Even worse, most of the bacteria identified contained resistance to one or more of 11 antibiotics used in the study.

Although there has only been one outbreak of illness linked to soda fountain machines on record, Renee Godard, lead author of the study and professor of biology and environmental studies at Hollins University, indicated that tainted beverages could cause isolated instances of food poisoning.  “There isn’t any major foodborne outbreak,” Godard said. “But soda fountain beverages could be linked to gastrointestinal upset that could go unreported. It’s simply that some bacteria may potentially cause some disease or gastroenteritis distress.”

Microbiologists involved in the study agreed with Godard’s assessment. Charles Gerba, a microbiologist at the University of Arizona, said he was not surprised to learn of coliform bacteria in soda fountain machines.

“We’ve seen it with drinking water dispensing machines where customers fill up jugs of water,” he said. “You see it anytime you have something where people can touch the dispenser.”

Philip Tierno, director of Clinical Microbiology and Immunology at New York University Langone Medical Center, shared the sentiment.

“Wherever man is there will be representation of feces. We’re basically bathed in feces as a society.”

Despite the compelling presence of bacteria, researchers have yet to pinpoint the source of origin. Few people observed during the study touched the nozzles of the soda fountain machines and managers interviewed by Godard reported cleaning the outside of the machines daily. This led Godard and her team to suspect bacteria growth on the plastic tubing inside the machines.

“Our best guess is they’re actually establishing themselves on the lining of the plastic tubing,” she said. “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.”

While manufacturers of soda fountain machines recommend that machine owners flush out the internal tubes once a month, Godard speculated that, “restaurant owners wouldn’t have the vaguest idea about how to flush those machines.”  As a result, bacteria could fester inside the damp plastic tubes.

Godard said she hopes the study will compel owners to adopt more sanitary cleaning techniques. “These findings have important public health implications,” the study concluded. “They signal the need for regulations enforcing proper hygienic practices associated with these beverage dispensers.”