Did Spores in Greek Yogurt Sicken Consumers or Not?

Ten months ago, the Greek yogurt company Chobani voluntarily pulled 35 flavors of its popular yogurt off supermarket shelves after the FDA received multiple consumer reports of gastrointestinal symptoms after eating mold-tainted yogurt. The number of reports reached more than 200.

At the time, Chobani said that the mold in question, Mucor circinelloides, was not considered a foodborne pathogen and was not dangerous to most customers, citing a comment from Cornell University professor of food science Randy Worobo: “This mold should not pose a health risk to most consumers. Very rarely, it can act as an opportunistic pathogen, but not through food and usually only for people with compromised immune systems through inhalation.”

But now, a new study from Duke researchers suggests that the particular strain of mold found in the yogurt was the most virulent subspecies, Mucor circinelloides forma circinelloides (Mcc), which they say can cause significant reactions in humans.

Soo Chan Lee, PhD, a post-doctoral fellow in Duke’s Center for Microbial Pathogenesis, obtained samples of the tainted yogurt from a couple in Texas who had experienced GI distress after eating a casserole made with the yogurt. “She searched online about this, found our research articles, and sent us samples of the yogurt.”

Dr. Lee’s group sequenced a several-genome area of the yogurt to identify the mold subspecies, and found Mcc; they then tested the virulence in mice by infecting them through the bloodstream; four of five mice infected that way died. “While information disseminated in the popular press would suggest this fungal contaminant poses little or no risk to consumers, our results show instead that it is capable of causing significant infections in animals,” they wrote.

On the other hand, when five diabetic mice received spores by mouth, there was little response; only one showed weight loss. “We did not otherwise see a pattern of symptoms,” says Dr. Lee. “So it’s not crystal clear that we can link the GI symptoms with the fungal contamination.”

Cornell’s Worobo says that the fact that oral-fed mice were almost symptom-free is very telling; the only significant pathogenic effects came when mice were exposed to the mold directly through the bloodstream, at a much higher inoculum (a million colony-forming units per mouse) than would ever occur in natural exposure.

“The study is interesting, but it has significant flaws,” he says. Ultimately, it doesn’t do much more than establish what I said at the time of the initial recall: This mold can be an opportunistic pathogen for people who are immunocompromised, but for healthy consumers, it shouldn’t pose a health risk unless you’ve had oral surgery, or there’s some other kind of ‘direct entry’ to the bloodstream.”

Chobani representatives have also raised questions about the study, calling it “highly irresponsible” and citing a “lack of scientific rigor.”

Chobani undertook an extensive cleanup after the recall, which both Dr. Lee and Worobo praised. “Consumers should understand that food industry sanitation efforts are not only to control foodborne pathogens, but also on non-pathogenic microorganisms, including fungus,” Worobo says. “Sanitation efforts for controlling fungal spoilage will control fungal pathogens as well.”

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