Stop washing those dishes!

The dishwasher, friend or foe?

Figure 1, sampling site in the dishwasher (arrow)

I’ve finally found a way to get out of washing the dishes at the YCPMicro household: apparently, household dishwashers are a hotbed of pathogens! This is via a new report from the research journal, Fungal Biology. Researchers at the University of Ljubljana in Slovenia examined 186 dishwashers in communities throughout Europe, North America, and South America for the presence of microorganisms. What they found is most alarming, and suggests that hot water with detergent may not be enough to keep the dishes clean.

Samples were collected by using sterile cotton swabs moistened with physiological saline, and returned to the laboratory for analysis. Swabs were then used to inoculate fungal media, and incubated for 1 week at 37 °C. Isolated colonies were analyzed by extracting DNA to use as a polymerase chain reaction (PCR) template for ribosomal gene amplification. The PCR amplicons were sequenced, and compared to DNA databases for strain identification. Isolated colonies were then examined for their growth temperature sensitivity, for their pH sensitivity, and for their sensitivity to varied salt conditions.

The researchers found that a number of fungal groups , including Aspergillus, Candida, Fusarium, Pichia, and Rhodotorula were frequently isolated from ‘clean’ dishwashers, indicating that the organism was readily surviving regular wash cycles. In vitro analysis of isolated organisms demonstrated a significant laboratory ability to tolerate temperatures, pH levels, and salt levels well away from normal, contributing to their ability to survive in the dishwasher environment. Many of these organisms are associated with human disease, particularly in those individuals susceptible to opportunistic infections.

Isolation of fungi was not an unexpected result to the researchers; fungi, particularly yeasts thrive in warm, moist environments, however the ability of those fungi to survive in the elevated temperatures with alkaline detergents was surprising. However, what the researchers found was the the fungi were being enriched within the dishwasher; bacterial species for instance were easily eliminated and were difficult to culture. It is important to note that many of the organisms recovered are not going to be hugely significant pathogens for the majority of the public. The ability of many of these organisms to cause disease is dependent on their gaining entry to the body via the parenteral route, or in an otherwise compromised host.

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About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on October 27, 2011, in Danger danger danger!, gross, Wash your hands!. Bookmark the permalink. 2 Comments.

  1. So as of now, there is no known way of avoiding these fungi in a dishwasher?

    • I would say yes. The main problem is for the otherwise immunocompromised, who shouldn’t be outside of their bubbles anyway. For the rest of us, constant immune stimulation makes us stronger, contrary to what the antivaxxers might say.

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