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Chobani blasts “irresponsible” study on moldy yogurt; authors stand by their paper

By Elaine Watson+

08-Jul-2014
Last updated on 09-Jul-2014 at 00:42 GMT

Professor: 'This type of experiment, while interesting, does not reflect natural exposure through foods'
Professor: 'This type of experiment, while interesting, does not reflect natural exposure through foods'

Dr Alejandro Mazzotta - the microbiologist heading up food safety at Chobani - says he is disappointed by the publication of a “highly irresponsible” paper in the peer-reviewed journal mBio alleging that the fungal contaminant found in some of its yogurts last fall was a potentially dangerous food borne pathogen.  

Meanwhile, Dr Randy Worobothe Cornell professor originally cited by Chobani as an expert at the time of the recall has also reaffirmed comments he made then that the contaminant in question should not pose a health risk to most consumers.

However, the paper’s authors told FoodNavigator-USA that their paper “was not written to be sensationalist, but to be a cogent and succinct summary of the findings presented” (click HERE to read it). 

Flawed methodology, poor use of citations, and general lack of rigor

Chobani first started fielding complaints about bloated/fizzy yogurt cups made at its Twin Falls plant in Idaho last August, and voluntarily recalled selected products on September 5 after confirming they had been affected by a "common mold".

Dr Mazzotta: There is no evidence, including the assertions presented in this publication, that the strain in the recalled products causes illness in consumers when ingested

At the time, Dr Worobo, professor of Food Science at Cornell University’s College of Agriculture and Life Sciences, said the contaminant was “not considered a disease-causing foodborne microorganism”.

However, the authors of the new mBio paper say the strain in question - Mucor circinelloides f. circinelloides - is the “most virulent M. circinelloides subspecies and is commonly associated with human infections”, while studies it had conducted on mice showed that it is "capable of causing significant infections in animals".

Injecting mice with fungus not the best way to determine how humans orally ingesting yogurt might respond

Speaking to FoodNavigator-USA  on Tuesday, Chobani’s VP quality, food safety, and regulatory affairs Dr Alejandro Mazzotta said he was surprised that the paper  made it through the peer review process owing to what he claimed to be its flawed methodology, poor use of citations, and general “lack of scientific rigor”, and for drawing conclusions that are not supported by the evidence presented.

Dr Mazzotta, who joined Chobani last October after a distinguished career working in senior food safety and quality roles at firms including McDonald’s, General Mills, and Campbell Soup, said alarm bells rang as he read that the authors of the study had tested yogurt from an opened cup of yogurt from a consumer that had allegedly fallen sick after eating it.

He added: “We don’t know how long the yogurt had been there, opened, whether the tests were conducted after the expiration date, what else it had been exposed to.”

Unnecessarily sensationalist

As for the methodology employed in the study, meanwhile, injecting large amounts of fungal spores directly into the bloodstream of mice is not the best way to determine how humans orally ingesting a small amount of yogurt might respond, he observed.

mBio study authors: 'The preponderance of evidence suggests that the presence of this fungus in the yogurt was responsible for documented cases of illness in humans who consumed the yogurt'

Meanwhile, statements the authors make early in the study that M. circinelloides is a food-borne pathogen that can cause lethal mucormycosis are not consistent with statements they make later in the study, where they note that the Mucho isolate "did not cause apparent disease symptoms” in the mice following oral ingestion, although the strain did survive the GI tract and was detected in fecal matter.

Finally the paper, which was unusual in that it called out a specific company/brand, is unnecessarily “sensationalist”, he claimed, given that the authors themselves acknowledge that "It is as yet unclear whether Mucor infection is directly responsible for the illnesses reported in the M. circinelloides outbreak related to the yogurts."

Dr Mazzott said he was also disturbed by the use of the word 'outbreak' to describe the contamination incident, given that the FDA had classified it as a class II recall (where there is a 'remote probability' of adverse effects, whereas class I refers to 'reasonable probability').

Dr Worobo L: This type of experiment does not reflect natural exposure through foods

Dr Randy Worobo: 'This type of experiment, while interesting, obviously does not reflect natural exposure through foods'

Meanwhile, Dr Randy Worobo told FoodNavigator-USA he also had concerns about the paper's conclusions: “While the data indicate that the isolates can cause disease when injected directly into the bloodstream of mice – at a level of 1 million Mucor circinelloides per mouse – this type of experiment, while interesting, obviously does not reflect natural exposure through foods.

“The authors also evaluated the ability of the Mucor circinelloides isolate from yogurt to cause disease in mice exposed orally. This did not provide any scientific evidence that the Mucor circinelloides isolate from yogurt can cause illness symptoms after oral exposure.

“With the lack of any clinical symptoms observed, one cannot conclude that the Mucho isolate has the ability to cause human disease after oral exposure. Any claims to the opposite, over-interpret the data.”

Study authors: These experiments were fully controlled, and subjected to rigorous independent peer review

Asked to respond to these comments, the mBio study co-authors Dr Soo Chan Lee and Dr Joe Heitman from the Duke University Medical Center told FoodNavigator-USA: “These experiments were fully controlled, and subjected to rigorous independent peer review and editorial review prior to acceptance and publication.”

Asked about the methodology, they said: “The murine models employed in our study are standard ones used frequently by investigators to study the virulence potential of microbes in an animal model.  These studies, and similar ones of related isolates, show that this fungal species is a pathogen in mice capable of causing lethal infection via this route of infection… The inocula used was fully appropriate for this model. 

Dr Joe Heitman: Both the FDA and Chobani previously asserted that this fungal species, Mucor circinelloides, was an environmental mold and not a risk for causing disease. Our studies suggest otherwise

“Both the FDA and Chobani previously asserted that this fungal species, Mucor circinelloides, was an environmental mold and not a risk for causing disease. Our studies suggest otherwise.”

M. circinelloides can be a food borne pathogen

Asked about whether it was accurate to describe M. circinelloides as a food borne pathogen, they said: “The findings reported from Chobani, the FDA, and our own studies all show that it was found in food.”

Asked if M. circinelloides can cause lethal mucormycosis [fungal infection], they added: “This is also clearly a true and accurate statement based on ample published peer reviewed studies. The only question that one can legitimately raise and one hopes address are what is the level of risk after consuming this pathogen?”

Finally they noted: “The preponderance of evidence suggests that the presence of this fungus in the yogurt was responsible for documented cases of illness in humans who consumed the yogurt. What is not clear is whether an infection per se was responsible, since it is conceivable that the fungus produces a toxin that caused illness in humans.

“If so, it is the toxin causing the symptoms and not an infection caused by the fungus.”

Chobani conducted an aggressive, statistically significant series of tests

But Chobani’s Dr Mazzotta added: “There is no evidence, including the assertions presented in this publication, that the strain in the recalled products causes illness in consumers when ingested.”

Chobani has spent a significant sum on hiring food safety experts and establishing improved procedures to ensure that such incidents do not happen again, said Dr Mazzotta, who said a pipe from a line that had not yet been commissioned at the Twin Falls plant had been confirmed as the cause of the incident.

Click HERE for more on this story.

Click HERE to read the mBio paper. 

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