Wednesday, July 9, 2014

Moldy Yogurt Can Make You Sick

In September of 2013, a manufacturer of Greek yogurt recalled product in September of 2013 due to the fact that consumers were complaining of mold in the product.  While it was claimed to be a spoilage mold, there were reported illnesses. 

Researchers discovered that the mold found in yogurt, Mucor circinelloides f. circinelloides, can cause illness.  While this organism is traditionally looked upon as a opportunistic pathogen, it can survive through the GI tract, as was seen in mice studies.  The researchers also indicated the potential to produce harmful metabolites, although Mucor circinelloides has not been known to produce mycotoxins.  According to the report, "This study demonstrates that M. circinelloides can spoil food products and cause gastrointestinal illness in consumers and may pose a particular risk to immunocompromised patients."

Now, it is hard to tell from this report whether there was an gastrointestinal  infection associated with these cases or people are just reacting to the metabolites produced by the mold.  Generally in past cases where infections have occurred in people, there have normally been underlying health issues in the person.  

So from a more simplistic viewpoint, when one eats food that has mold that shouldn't be there, there is a good possibility it is going to give one an upset stomach, at the least.  Molds will produce metabolites within the food, or even in the gut, that can cause an adverse reaction.  Certainly some molds will be worse than others...some can produce really bad metabolites, some that have been categorized as mycotoxins, while others can cause infections, especially in high risk individuals.

It is interesting to point out, that manufacturer of the yogurt product has been critical of this report.

Consumers - Don't eat food that has mold that shouldn't be there, especially if you are in a high risk group.
Producers and processors - prevent food from unwanted mold...most of this can be prevented through good sanitation, but processing controls may also be needed.

Analysis of a Food-Borne Fungal Pathogen Outbreak: Virulence and Genome of a Mucor circinelloides Isolate from Yogurt

Soo Chan Leea, R. Blake Billmyrea, Alicia Lia, Sandra Carsonb, Sean M. Sykesc, Eun Young Huhd, Piotr Mieczkowskie, Dennis C. Koa,f, Christina A. Cuomoc, Joseph Heitmana + Author Affiliations
aDepartment of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, USA
bDental Department, Corpus Christi State Supported Living Center, Corpus Christi, Texas, USA
cBroad Institute of MIT and Harvard, Cambridge, Massachusetts, USA
dDivision of Gastroenterology and Hepatology, Center for Gastrointestinal Biology and Disease, University of North Carolina at Chapel Hill, North Carolina, USA
eDepartment of Genetics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA
fDepartment of Medicine, and Center for Human Genome Variation, Duke University Medical Center, Durham, North Carolina, USA
Address correspondence to Joseph Heitman,, or Soo Chan Lee,
Editor Fran├žoise Dromer, Institut Pasteur


Food-borne pathogens are ongoing problems, and new pathogens are emerging. The impact of fungi, however, is largely underestimated. Recently, commercial yogurts contaminated with Mucor circinelloides were sold, and >200 consumers became ill with nausea, vomiting, and diarrhea. Mucoralean fungi cause the fatal fungal infection mucormycosis, whose incidence has been continuously increasing. In this study, we isolated an M. circinelloides strain from a yogurt container, and multilocus sequence typing identified the strain as Mucor circinelloides f. circinelloides. M. circinelloides f. circinelloides is the most virulent M. circinelloides subspecies and is commonly associated with human infections, whereas M. circinelloides f. lusitanicus and M. circinelloides f. griseocyanus are less common causes of infection. Whole-genome analysis of the yogurt isolate confirmed it as being close to the M. circinelloides f. circinelloides subgroup, with a higher percentage of divergence with the M. circinelloides f. lusitanicus subgroup. In mating assays, the yogurt isolate formed sexual zygospores with the (−) M. circinelloides f. circinelloides tester strain, which is congruent with its sex locus encoding SexP, the (+) mating type sex determinant. The yogurt isolate was virulent in murine and wax moth larva host systems. In a murine gastromucormycosis model, Mucor was recovered from fecal samples of infected mice for up to 10 days, indicating that Mucor can survive transit through the GI tract. In interactions with human immune cells, M. circinelloides f. lusitanicus induced proinflammatory cytokines but M. circinelloides f. circinelloides did not, which may explain the different levels of virulence in mammalian hosts. This study demonstrates that M. circinelloides can spoil food products and cause gastrointestinal illness in consumers and may pose a particular risk to immunocompromised patients.

IMPORTANCE The U.S. FDA reported that yogurt products were contaminated with M. circinelloides, a mucoralean fungal pathogen, and >200 consumers complained of symptoms, including vomiting, nausea, and diarrhea. The manufacturer voluntarily withdrew the affected yogurt products from the market. Compared to other food-borne pathogens, including bacteria, viruses, and parasites, less focus has been placed on the risk of fungal pathogens. This study evaluates the potential risk from the food-borne fungal pathogen M. circinelloides that was isolated from the contaminated commercial yogurt. We successfully cultured an M. circinelloides isolate and found that the isolate belongs to the species M. circinelloides f. circinelloides, which is often associated with human infections. In murine and insect host models, the isolate was virulent. While information disseminated in the popular press would suggest this fungal contaminant poses little or no risk to consumers, our results show instead that it is capable of causing significant infections in animals.


Citation Lee SC, Billmyre RB, Li A, Carson S, Sykes SM, Huh EY, Mieczkowski P, Ko DC, Cuomo CA, Heitman J. 2014. Analysis of a food-borne fungal pathogen outbreak: virulence and genome of a Mucor circinelloides isolate from yogurt. mBio 5(4):e01390-14. doi:10.1128/mBio.01390-14.

This article is a direct contribution from a Fellow of the American Academy of Microbiology.
Received 28 May 2014
Accepted 2 June 2014
Published 8 July 2014
Copyright © 2014 Lee et al.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-ShareAlike 3.0 Unported license, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

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