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The disease-causing fungi that lurk in your dishwasher

Researchers have found that dishwashers are particularly conducive to the growth and spread of disease-causing fungi. These fungi have been implicated in causing lung diseases and sometimes fatal infections…

This fungus is pretty harmless, but its tiny cousins are not. Bart Everson

Researchers have found that dishwashers are particularly conducive to the growth and spread of disease-causing fungi. These fungi have been implicated in causing lung diseases and sometimes fatal infections, especially among those with weak immunity.

Fungi come in many different forms. According to a study published this month and another published in 2011, the culprits in dishwashers are black yeasts (Exophiala), red yeasts (Rhodotorula), a white yeast (Candida parapsilosis), and some nasty moulds. These fungi make spores to survive in extreme environments, as well as to reproduce and spread. These spores are single-celled seeds that are very light and spread easily, through air or by clinging to moving things.

Species of Exophiala, have been shown to cause lung disease in patients with weak immunity, according to recovered clinical samples in the US. The mould Magnusiomyces capitatus can cause fatal infections in especially leukemia patients. Both red yeast, Rhodotorula, and the white yeast, Candida parapsilosis, are emerging disease-causing fungi, especially through infected catheters.

What makes fungi hard to deal with it is that they can survive almost anywhere and under extreme conditions. All they need is a little bit of moisture, even if it is in the form of humidity in the atmosphere.

Not so clean after all. bryan birdwell

It should not be surprising then that fungi prefer dishwashers. Not only are they damp and warm, the continuous use of detergents makes the environment favourably alkaline too. According to researchers, the rubber seals of dishwasher doors are the perfect places for these fungi. They are of course also found in natural environments like tropical rain forests, on tropical fruits, hot springs in Thailand, Japanese house baths and Turkish public baths.

In particular, species of the black yeast Exophiala and the mould Magnusiomyces capitatus also grow in high concentrations of salt, which tend to be maintained in dishwashers to avoid accumulation of calcium.

In the 2011 study, European investigators sampled 189 dishwashers from around the world. The presence of some mould or yeast could be detected in about 62% of these samples. The researchers also found that the calcium-content of water seemed to play a role in the growth and persistence of the black yeasts in the dishwashers, which agreed with earlier evidence. Using scanning electron microscopy, they showed that black yeasts excreted polymeric substances that formed a tough biofilm protecting the fungi from excess heat and mechanical damage.

In the most recent study, Turkish investigators sampled 153 dishwashers, in addition to other appliances, and found similar results. Almost one in five dishwashers yielded fungi, mostly black yeasts. These researchers also studied the genetic signatures of these black yeasts, and found one type that had specialised in invading urban households.

To clarify, there is yet no direct relationship established between dishwashers and human fungal infections, but the health hazard exists. Today, many patients have weakened immunity; even healthy individuals may have some undetected impairment in immunity because of the environment we live in. There is evidence of association between mould-infested “sick” buildings and human disease, especially respiratory illness. The recent outbreak of meningitis due to medication contaminated by a black mould (Exserohilum rostratum) was traced to poor maintenance of sterility in a US pharmacy. A continued co-existence with the fungal jungle in one’s own household could become a serious public health concern.

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14 Comments sorted by

  1. George Michaelson

    Person

    Judging by the dead cockroaches I find inside my dishwasher, they are pretty yummy for the top feeders.

    Judging by the dead gecko I found once in my dishwasher, the real top feeder thinks the cockroach sauna is pretty good for late night snacks.

    I just don't feel quite the same about this lovely dish storage device I have. wet, yummy, warm, tasty dirty dishes. Come and get 'em

    (I think I'll pack and run and empty from now on)

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  2. Khalil A. Cassimally

    Community Coordinator at .

    Ok, so is there anything we can do to at least curb the spread of those fungi in the dishwasher?

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    1. Kausik Datta

      Post-doctoral Fellow at Johns Hopkins Medicine

      In reply to Khalil A. Cassimally

      Cleaning the rubber seals of the dishwasher regularly is an effective deterrent to fungal growth. An acidic solution such as vinegar may help, but the important idea is not to allow moisture to accumulate. If the door is periodically left open, moving air currents are generally effective as a desiccator, which prevents spores from growing.

      It is important to remember that fungi are ubiquitous in the environment and cannot be avoided; many kitchens, washrooms, boiler-rooms etc. have yielded similar fungal microbes in the past. Yet, we don't always fall ill with clockwork regularity, because our immune systems are efficient at combating such external malefactors. As medical science progresses, we have better medications as well to combat such diseases.

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  3. Trent Yarwood

    Infectious Diseases Physician, Associate Lecturer at University of Queensland

    Microbes of all sort live everywhere in the environment. This isn't particularly surprising, and moulds are known to like moist, damp environments.

    Given you state that there is no known link from finding these organisms in dishwashers to human disease, I can't help wondering what the point of the article is?

    Diseases caused by many of these fungi are rare even for immunosuppressed patients (I've seen two people with Exophiala in five years and one person with Mucor), who are much more likely to get a serious infection from one of the bacteria that live in their intestine or a healthcare associated IV-line infection than any of these diseases.

    Awareness is a great idea. Drawing attention to an environmental reservoir that hasn't yet been implicated in causing an extremely rare disease skirts the line between awareness-raising and sensationalist germ-panic.

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    1. Kausik Datta

      Post-doctoral Fellow at Johns Hopkins Medicine

      In reply to Trent Yarwood

      Thank you for your comment, Dr. Yarwood. You reiterate an important idea that needs to be borne in mind - that microbes of all descriptions are everywhere in the environment. However, I sense a disturbance in the Force - pardon my flippancy - when an Infectious Disease physician questions the motive behind raising awareness and keeping a high index of suspicion.

      I shall leave you with two points:
      (a) You have seen two Exophiala cases in 5 years and 1 person with mucor in Queensland, I presume…

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    2. Trent Yarwood

      Infectious Diseases Physician, Associate Lecturer at University of Queensland

      In reply to Kausik Datta

      My work primarily deals with antimicrobial resistance; Australia has a relatively high use of antibiotics compared to other countries.

      One of my personal biases is that community (and doctors) attitude towards the risks of infection contribute to driving this high level of prescription and concern about infectious disease (as well as the sale of antimicrobial handwash and other domestic products which are not needed around the home and contribute to resistance).

      I've discussed this about…

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    3. Kausik Datta

      Post-doctoral Fellow at Johns Hopkins Medicine

      In reply to Trent Yarwood

      Your discipline is an august one. Rational use of antibiotics and adherence to policies which guide such use are excellent and necessary measures that significantly impact public health. On the other hand, I am sure you know fully well that antifungals are not administered willy-nilly like antibacterial antibiotics tend to be. Generation of secondary adaptive anti-fungal resistance in fungal pathogens of clinical significance is a relatively less encountered phenomenon. Therefore, I'm not sure I agree with this particular concern of yours in the context of the posted article.

      I'd like to assure you that I understand where you are coming from, but I guess I'd have to agree to disagree with you on the possible implications of raising awareness in this regard.

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  4. Don Harrod

    Forklift operator

    By not providing even the slightest hint of how to ameliorate this alleged problem, the author of this article proves he is any one (or more) of the following: Pandering, Inept, Sensationalistic, Desperate for clicks, Uneducated, Paid by the word, Melodramatic and Unfeeling.

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    1. Kausik Datta

      Post-doctoral Fellow at Johns Hopkins Medicine

      In reply to Don Harrod

      Thank you for your comment, Don. A tad harsh, but that's all right. I also notice the peculiar turn of phrase you used there - "how to ameliorate of this alleged problem". To me, this is not a merely "alleged" problem; I have used the term 'public health hazard' or risk, and yes, the risk exists, and that risk is the problem.

      How to treat a fungal infection is advice only your physician can provide you with. Dishing out medical advice is not the purpose of this essay. The only amelioration I…

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  5. Bethany S.

    Analyst

    Is it possible to get more details regarding this article's photograph? Specifically, what is the fungus and what exactly is it growing on? Thanks.

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