Soda fountains may dispense more than Diet Coke and Dr. Pepper, according to new research to be published this month in the International Journal of Food Microbiology. In an analysis of 90 soda and water samples taken from fountains in 30 different fast food restaurants in the Roanoke Valley region of Virginia, researchers from Hollins University found that 48% tested positive for coliform bacteria, or bacteria found in human and animal feces, 11% tested positive for Escherichia coli, and more than 17% tested positive for Chryseobacterium meningosepticum, which has been shown to cause pneumonia and even meningitis in people with compromised immune systems. So, how are these microbes ending up in our cokes? And, what does it mean for public health?
According to standards established by the Environmental Protection Agency (EPA), the public water supply cannot have a heterotrophic plate count (HPC)—or basic concentration of microorganisms—higher than 500/ml. (In Europe, the standard is 100/ml.) Yet, the researchers point out, there are no government regulations in place for the liquids dispensed from soda fountains. In this study, 20% of water and soda samples had HPC counts higher than 500/ml.
So, how are those bugs getting into the soda supply? As part of the study, researchers observed people using soda fountains to determine whether bacteria might be introduced by touching nozzles with their fingers. But, of the 281 people observed, only 5 (or 1.8%), actually nudged the nozzles. What’s more, even people who got refills seldom touched the nozzles with their used cups—only 2 of 47 (or 4.2%). Amy S. White, a biologist at Hollins and lead author of the study, says she was surprised. “That was our first guess. I would have guessed that this was hand-touching—I thought that kids or people were putting their hands on the nozzles, but it’s actually a really small population.”
Understanding how the bacteria enter the soda fountain is key, White says, because once it’s introduced, it can thrive and multiply in what is effectively a closed system. In the study, White and colleagues found that soda samples collected in the morning had far higher levels of bacterial contamination than those collected later in the day, something she hypothesizes likely has to do with the fact that, overnight, as the plastic tubes feeding the fountain aren’t being regularly flushed, bacteria can take hold and grow. “What we think is happening is that there are communities of bacteria living in those tubes inside those machines—a biofilm,” she explains. “As the machine gets used, the top layers of the biofilm get washed out.” But, when few people are buying sodas, the liquid isn’t being flushed through the tubes. “Overnight they multiply—and most bacteria can double every 20 minutes—so it doesn’t take long for a whole lot of organisms to grow.”
If it isn’t likely down to customers putting dirty fingers on the nozzles, though, what could be introducing the bacteria that ultimately may be creating this biofilm? White and colleagues confirmed that the municipal water supply met all EPA regulations, and that there were no outbreaks during the study period, so the bacteria wasn’t likely coming from the water. And sodas purchased in plastic bottles that were tested as controls showed no microbial contamination, so it wasn’t likely the syrup. Previous research had found similar problems—where clean water entered a fountain but contaminated water came out—leading White and colleagues to believe that it was in fact the soda fountains, but where were these bacteria coming from?
In a follow-up study, researchers interviewed 10 fast food restaurant managers about their cleaning routines for the soda fountains. Though the manufacturer of the fountain most frequently used in the locations studied suggests flushing the system and washing the nozzles with sanitizing solution once a month, of the 10 managers interviewed, only one said that the supply lines were regularly flushed with sanitizer.
What’s more, White says, any time an employee handles the tubes—to replace the soda syrup for example—they may introduce bacteria, and the actual cleaning process could even be part of the problem. “It could be handling of the nozzles [by employees],” she says. “Workers at the fast food restaurants take the nozzles off overnight, and soak them—some in disinfectant, which is great, but some in water,” which, she explains, does nothing to kill bacteria and may even provide an ideal breeding ground. Then, the next morning, “they take their hands and put them back on the machine.”
So, how worried should we be? “I’m not telling people to quit drinking soda,” White says, but she does believe that the presence of E. coli in more than 11% of samples—and in soda fountains at 13% of restaurants included in the study—is cause for concern, as is the presence of Chryseobacterium meningosepticum, which could prove dangerous for individuals with compromised immune systems. Additionally, while the presence of some coliforms in our environment is natural—as anyone who has seen the toothbrush experiment on Mythbusters will know—the concentrations found in the soda samples were far higher than you should expect to encounter in a normal environment. White emphasizes the importance of some exposure to bacteria in order to develop a healthy immune system, but suggests too that “poison is in the dose.” Additionally, she says that, “Coliform bacteria are indicator organisms, we use those to indicate that the sample may be contaminated with fecal material,” she says, but also to indicate the presence of larger groups of bacteria.
Additionally, many of the bacteria found in the soda samples—which included Coke, Pepsi, Diet Coke and Diet Pepsi—were resistant to antibiotics tested in the lab. One or more bacteria showed resistance to 7 out of 11 antibiotics tested, a finding White says is illustrative of a larger societal problem of growing antibiotic resistance.
So, where do we go from here? White says it’s a question of prevention. “Do we wait until [an outbreak of waterborne illness] happens, or do we see that there is a potential and regulate it now?” In Roanoke, White says the local public health authority has said it will look into the protocol for overseeing soda fountain sanitation, but that she has yet to hear anything more. The common sense answer is simply to “mandate and monitor the cleaning of these machines,” she says, adding, “Because it’s better to prevent disease than treat disease.”