Fungi in the Dishwasher

Since the 2012 outbreak of meningitis caused by steroid shots tainted with fungi, the danger of fungal contamination has become an increasing public health concern.

In a study published this month in Medical Mycology, and another published in 2011 in Fungal Biology, researchers took samples from household dishwashers in Europe, Asia, the Middle East, Africa, Australia, and North and South America.

They found that the high-temperature, moist, alkaline environment in dishwashers is the perfect habitat for some opportunistic fungal species known to be harmful to humans.

The yeast-like species they found most often were Exophiala (black yeasts), Rhodotorula (red yeasts), and Candida parapsilosis (white yeasts).  

According to the 2011 study, “Sixty-two percent of the dishwashers were positive for fungi, and 56 percent of these accommodated Exophiala.” The black yeasts Exophiala dermatitidis and Exophiala phaeomuriformis were most frequently identified.

Fungi are primitive plant organisms that reproduce by sending tiny spores out into the air. These microscopic spores can be easily inhaled into the lungs, where they can colonize and cause systemic infections that are difficult to cure.

Adults and children taking antibiotics and those with compromised immune systems are especially vulnerable to mycoses (fungal infections) in the lungs or on the skin. Exophiala species frequently infect the lungs of patients with cystic fibrosis. And diabetics are prone to developing fungal skin infections, which can cause dry, itchy rashes.

Both Rhodotorula and Candida are emerging problems in hospitals where contaminated catheters cause dangerous bloodstream infections in extremely sick patients, especially those in intensive care units. According to the U.S. Centers for Disease Control and Prevention (CDC), Candida is the fourth most common cause of hospital-acquired blood infections in the U.S.

Dishwashers, Perfect Habitats for Fungi

Modern households are ideal environments for growing fungi, especially damp areas like bathrooms, refrigerators, and dishwashers. However, dishwashers provide the perfect habitat.

Fungi can survive almost anywhere and under extreme conditions, showing remarkable tolerance to cold, high concentrations of salt, harsh detergents, and high temperatures.

According to the researchers, the rubber seals of dishwasher doors are perfect places for thermophilic (heat-loving) black yeasts to grow. Species of the black yeast Exophiala also thrive in environments with high concentrations of salt, an ingredient found in dishwasher soap that is used to reduce calcium buildup.

How to Kill Fungi in Your Dishwasher

Baking soda, vinegar, and bleach may help to kill mold, mildew, and fungi growing on the inside surfaces of your dishwasher. This cleaning regimen should be done once per month to prevent fungi from taking hold.

Start by removing all racks and washing them by hand in hot soapy water. Use a soapy sponge to wipe down the dishwasher's interior surfaces and around the rubber door seal. Let everything air dry thoroughly.

Combine a half cup of white vinegar with 2 cups of hot water in a spray bottle. Spray all surfaces thoroughly and scrub with an old toothbrush around the crevices and seal. Use a scrub brush for large surfaces.

Put the racks back into the dishwasher. Fill a small glass bowl with vinegar and place it on the top rack. Run the washer on the hottest setting. Sprinkle 1 cup of baking soda on the dishwasher floor and run the machine a second time on high heat.

Finish by running the washer with a commercial dishwasher cleaner, followed by hand cleaning all surfaces with a four-to-one mixture of hot water and bleach.

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