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Last year's recall of moldy Chobani Greek yogurt turned into a marketing nightmare for the company, which tried to put the best face on it by saying that the mold was naturally occurring and not considered a food-borne pathogen.

Not so, say Duke University researchers who studied samples taken from the recalled yogurt. They say the mold was the most virulent form of a fungus called Mucor circinelloides, which is "highly pathogenic" and could cause serious infections in immune-compromised consumers.

Chobani questioned the Duke findings.

“In regards to this specific study, we were just made aware of it and want to take more time to review its methodology and assertions. To our knowledge, there is no evidence, including the assertions presented in this publication, that the strain in the recalled products causes illness in consumers when ingested," said Dr. Alejandro Mazzotta, Chobani Vice President of Global Quality, Food Safety, and Regulatory Affairs

“Chobani conducted an aggressive, statistically significant series of tests of the products voluntarily recalled in September 2013 with third party experts confirming the absence of foodborne pathogens. Chobani stands by these findings, which are consistent with regulatory agency findings and the FDA’s Class II classification of the recall on October 30th 2013,” Mazzotta said.

More serious threat

The study, which appears July 8 in the online, open access journal mBio, indicates that the particular strain of fungus found in the yogurt may pose a more serious threat to public health than previously thought, said Dr. Joseph Heitman, a senior author of the study and professor and chair of molecular genetics and microbiology at Duke's School of Medicine.

Heitman said the finding also suggests specific attention should be paid to fungal pathogens in food products and the factories that manufacture them.

"Typically when people think about food-borne pathogens, they think about viruses or bacteria, they don't think of fungi," said Soo Chan Lee, a senior research associate at Duke who led the study. "Our research suggests it may be time to think about fungal pathogens and develop good regulations to test them in manufacturing facilities."

Casserole clue

The study relied on a sample provided by a Texas couple who became ill with diarrhea and vomiting after eating a casserole made with the recalled product. The couple said the casserole containing the yogurt had been cooked for more than 30 minutes at 350 degrees Fahrenheit. They both reported experiencing diarrhea and the man said he also vomited after eating the casserole a second time.

After learning of the recall, the couple contacted the Heitman laboratory -- which had previously published papers on Mucor circinelloides -- and offered the remaining portion of their yogurt for analysis. They said the tub of plain yogurt had been kept in their refrigerator at 37 degrees Fahrenheit for several days, but it showed half-inch to one-inch colonies growing on its surface.

The Heitman lab provided the couple with instructions and a kit to collect swab samples from the yogurt in Texas and then to ship both the swabs and the container cold to North Carolina. Both the swabs and the tub sample produced colonies of the pathogenic mold in the lab.

The Duke researchers isolated Mucor circinelloides from the yogurt container and applied DNA barcoding -- analyzing standardized regions of the fungal genome -- to further identify its exact subspecies. They found it belonged to the most virulent subspecies, Mucor circinelloides forma circinelloides (Mcc).

"There are three closely related species, and one of them we typically find infecting humans," Heitman said. "There was some chance that this yogurt isolate would be the human pathogenic form, and we found that it was."


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