The fungus responsible for an outbreak of contaminated Greek yogurt last year is not harmless after all but a strain with the ability to cause disease, according to research published in mBio®, the online open-access journal of the American Society for Microbiology.
In September 2013, customers of Chobani brand Greek yogurt complained of gastrointestinal (GI) problems after consuming products manufactured in the company's Idaho plant. The company issued a recall, and it was believed at the time that the fungal contaminant Murcor circinelloides was only a potential danger to immunocompromised individuals. However, as complaints of severe GI discomfort continued from otherwise healthy customers, researchers began to question the fungus and its ability to cause harm in healthy humans.
"When he heard about the Chobani recall after reports of people becoming sick from yogurt contaminated with Murcor circinelloides, we thought the M. circinelloides strain could cause more serious problems than one might think." says Soo Chan Lee of Duke University, an author on the study.
In the study, the researchers isolated a strain of the fungus from a yogurt container that was subject to recall. Using a technique known as multi-locus sequence typing (MLST), they identified the strain as Mucor circinelloides f. circinelloides (Mcc). Unlike other strains of the fungus, that particular subspecies is commonly associated with human infections.
Whole-genome sequence analysis of the yogurt isolate confirmed it as being closely related to Mcc and also revealed the possibility that this fungus could produce harmful metabolites that were previously unknown in this species. The researchers then tested the strain on mice, where the fungus showed an ability to cause lethal infections when the fungal spores were injected into the bloodstream as well as to survive passage through the GI tract when the spores were ingested orally.
"When people think about food-borne pathogens, normally they list bacteria, viruses, and maybe parasites. Fungal pathogens are not considered as food-borne pathogens. However, this incidence indicates that we need to pay more attention to fungi. Fungal pathogens can threaten our health systems as food-borne pathogens" says Lee.