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."
The researchers then performed a number of experiments to assess the virulence of the fungal contaminant.
When they injected spores from the fungus into the bloodstream of mice via their tail vein, they found it produced a lethal systemic infection in four out of five diabetic mice, which were being used as a model of one of the major risk factors for human infection. However, when they fed spores by mouth to five diabetic mi
|Contact: Karl Leif Bates|