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Your dishwasher is an “extreme environment” for germs, but bacteria and fungi can still grow near where you clean your glasses, utensils and plates, researchers reported Friday.
“These appliances can present a source of domestic cross-contamination leading to broader medical impacts,” the Danish, Slovenian and Belgian scientists wrote in a study published in the journal Applied and Environmental Microbiology.
But most people shouldn’t worry about getting sick “unless you’re licking” parts of the machine, said Philip Tierno, professor of microbiology and pathology at the NYU School of Medicine and author of “The Secret Life of Germs.”
“If you do the same test on a shower head or other area in the house, including the sink drain, you’ll find a myriad of organisms very similar to this,” Tierno, who was not involved in the study, told TODAY.
“Microbes colonize and cover and coat everything on the planet, so it’s not unusual that you’re going to find organisms.”
For the paper, the researchers tested the rubber seals of 24 different dishwashers in homes across Slovenia. All had a biofilm — a slimy colony of microorganisms — clinging to the surface. That’s not unusual since you will tend to find a biofilm whenever there’s water, said Tierno.
Even though high temperatures, detergents and jets of water in dishwashers make things tough for microorganisms, germs still grew.
The types of bacteria most commonly found in the samples were pseudomonas, escherichia and acinetobacter — common bugs that can be found in everybody’s house, Tierno said.
No pathogens were found — only groups of bacteria to which pathogens belong, said Charles Gerba, professor of microbiology and environmental sciences at The University of Arizona, who was not involved in the study.
The most common types of fungi found were candida, cryptococcus and rhodotorula, some of which are indigenous to people and animals, while others are environmental, Tierno noted.
The types and variety of bacteria found varied depending on the age of the dishwasher and how often it was used, but the authors did not weigh in on whether this created a riskier or safer environment.
The type of tap water also played a role, with dishwashers that used hard water home to a bigger variety of fungi, the researchers wrote. Hard water has different minerals that can make organisms adhere better, Tierno said.
“I do not see anything to worry about for a normal healthy person,” Gerba said.
If you’re immuno-suppressed, the biofilm may contain organisms that theoretically might cause you harm, Tierno noted. But unless you’re wiping your dishes across the seal or licking the seal, you’re not coming in contact with it.
Even if you did, “under most circumstances, your body can handle these environmental organisms and even some that are indigenous to people without a problem,” Tierno said. “I would not worry. I would just pay attention to cleaning.”
How to clean:
Tierno recommends using a 10 percent bleach solution to clean around the rim where the seal is. To make it, mix one part bleach with nine parts water. He uses the same solution plus soapy water to clean the bottom and sides of his dishwasher to prevent any build-up of debris. Do this weekly and you’ll be free of any major problem.
House-maintenance expert Bob Vila recommends cleaning your dishwasher once a month with a three-step process that includes a vinegar wash to get rid of grease and odors. Simply place a cup of white vinegar in a dishwasher-safe container on the upper rack of an empty dishwasher and then run the machine through a hot-water cycle. See all three steps in this guide.