Experts Say Molds, Yeasts, Other Germs Are Living in Your Coffee Machine

reservoirs and pot handles are among most germ-filled components

By Jonny Lupsha, Wondrium Staff Writer

Fungi and bacteria thrive in and around coffee makers at home and work, according to USA Today. During an NSF International study, half of coffee machine reservoirs tested positive for mold or yeast. Here’s what’s in your coffee besides coffee.

Man pouring homemade coffee in kitchen
Coffee makers at home and at the office should regularly be cleaned per the manufacturer’s recommended cleaning instructions. Photo by Aleksandra Suzi / Shutterstock

Unless you regularly clean your coffee machine inside and out, it could be a breeding ground for bacterial growth and fungi. “Chuck Gerba, professor of microbiology at the University of Arizona, said coffee break rooms have more bacteria than restrooms in most office buildings,” the USA Today article said. “If the office has a coffee pot, Gerba says the first thing that gets germiest [sic] is the coffee pot handle. However, on a single-use machine, he says the top of the machine where the people place the plastic pod has the most germs.”

As unappetizing as these basic lifeforms are, getting to know them can assist in understanding the risks they pose.

Molds and Yeasts on the Surface

Molds and yeasts are two types of fungus with fundamental differences used to categorize them as one or the other.

“Molds are actually composed of many hyphal elements,” said Dr. Barry C. Fox, Professor of Infectious Disease at the University of Wisconsin School of Medicine and Public Health. “Hyphae are threadlike, branching tubules composed of fungal cells attached end to end. A yeast is a unicellular growth form of fungal growth; these cells can appear spherical or elliptical.”

Superficial fungal infections come with the nickname “tinea,” Dr. Fox said, and often have other common monikers. Ringworm is really a fungal infection called tinea corporis, despite the nickname containing the word “worm.” Similarly, the clinical name for athlete’s foot is tinea pedis.

Dr. Fox said that subcutaneous fungal infections—those just under the skin—are usually caused by a fungus entering the body after an injury to the skin, but not always.

“One important yeast that can cause an either superficial or subcutaneous fungal infection is known as Candida albicans,” he said. “Candida species, like bacteria, are part of the body’s normal microbiota. When antibiotics can kill the bacteria but not the yeast, candida can take over and expand their growth without competition.”

Common examples include diaper rash in babies, oral thrush after antibiotic therapy, and “overgrowth in the vaginal area after antibiotics while leading to a white discharge,” according to Dr. Fox.

Complications of Fungal Infections

Although unpleasant, superficial and subcutaneous fungal infections aren’t usually serious unless they lead to a disease that spreads throughout the body. The three most common of these, in humans, are histoplasmosis, blastomycosis, and coccidioidomycosis. Dr. Fox said that all three are “dimorphic fungi,” meaning they grow in the laboratory as molds but in the body as yeasts.

“What is unique about these three fungal diseases is that they characteristically inhabit unique geographic areas of the United States, and hence are called endemic mycoses,” he said. “Histoplasmosis and blastomycosis are commonly found in the drainage area of the Mississippi River Valley, but isolated cases of both diseases may occur in other parts of the country. Coccidioidomycosis is unique to the southwestern United States including Arizona, New Mexico, and southern California.”

Other potentially serious fungal infections persist nationwide. Dr. Fox mentioned Cryptococcus neoformans, a yeast found in soil throughout the United States. “When inhaled by patients with compromised immune systems [it] can lead to pneumonia and serious infection around the brain and spiral cord, known as fungal meningitis,” he said.

A single pharmaceutical compounding center infected with Exserohilum caused a multistate outbreak of fungal meningitis and infectious arthritis in September 2012. Seven hundred people received steroid injections from its supply and contracted meningitis or spinal infections.

“The Tennessee Department of Health sounded the alarm based on a telephone call from an alert clinician treating a patient with this unusual form of meningitis,” Dr. Fox said. “With information rapidly communicated from Tennessee, the Centers for Disease Control reached out to state and local health officials and took collective action. Within days, the source of the outbreak was identified and a massive effort was undertaken to identify and contact nearly 14,000 potentially exposed patients and their physicians across 23 states.”

Unfortunately, the outbreak caused many deaths and left many patients with long-term disabilities.

If it’s been a while since you’ve cleaned out your coffee machine, it may be time. Although many fungal infections are easily treatable, some are serious and even fatal.

Image of Professor Barry Fox, M.D.

Dr. Barry C. Fox contributed to this article. Dr. Fox is a Clinical Professor of Infectious Disease at the University of Wisconsin School of Medicine and Public Health. He received his undergraduate degree in Molecular Biophysics and Biochemistry from Yale University and his medical degree from Vanderbilt University.