July 9, 2014
Virulent Fungus Discovered In Recalled Chobani Yogurt Products
Brett Smith for redOrbit.com - Your Universe Online
"Typically when people think about food-borne pathogens, they think about viruses or bacteria, they don't think of fungi," said study author Soo Chan Lee, a senior research associate at Duke University. "Our research suggests it may be time to think about fungal pathogens and develop good regulations to test them in manufacturing facilities."
The study was based on a single case, a Texas couple who became ill after eating a casserole made with the recalled product. The couple said the casserole had been cooked for over 30 minutes at 350 degrees F. They both said they had diarrhea and the man said he also vomited after eating the casserole again.
The study tested the couple’s tub of plain yogurt that had been stored in their fridge at 37 degrees F, yet had half-inch to one-inch colonies growing on its surface. After using DNA barcoding technology, the team was able to identify its exact subspecies – the most virulent strain, Mucor circinelloides forma circinelloides (Mcc).
"There are three closely related species, and one of them we typically find infecting humans," said study author Joseph Heitman, a professor of molecular genetics and microbiology at Duke. "There was some chance that this yogurt isolate would be the human pathogenic form, and we found that it was."
To assess the virulence of the strain, the team injected spores from the fungus into mice via their tail vein, they discovered it produced a deadly infection in four out of five diabetic mice, chosen as a model for the system of immune-compromised humans. However, when mice were given spores by mouth, it resulted in serious weight loss in only one out of five cases.
The researchers also found that the fungus survived passage through the gastrointestinal tract of the mice, suggesting it could opportunistically colonize an immune-compromised host.
"We still don't know if the fungus is infecting the gastrointestinal tract, or if it is producing some sort of toxin that makes people sick," Heitman said.
The scientists sequenced the complete genome of the fungus to check for clusters of genes that could create toxic molecules called secondary metabolites. Even though they uncovered a quantity of candidates, the team wasn't certain if the fungus is making any toxins that could clarify the symptoms felt by people who consumed the contaminated yogurt.
The team also tested 16 other samples of Chobani yogurt and did not find Mucor circinelloides in any of them. The scientists asked the FDA for more data on its analyses of the recalled product or access to the samples the agency had acquired. The agency denied their requests.