Hundreds of viruses live on showerheads and toothbrushes

Hot showers are great, but you're not the only organism bathing in the warming wash of water — new research from the US has found diverse communities of viruses are dwelling on your showerhead too.

Apparently, that's good news.

"The number of viruses that we found is absolutely wild," said Erica Hartmann of Northwestern University, a microbiologist who led the study.

"We found many viruses that we know very little about and many others that we have never seen before. It's amazing how much untapped biodiversity is all around us. And you don't even have to go far to find it; it's right under our noses."

Or bathroom faucets, it seems.

Viruses are most often associated with the diseases they cause in humans and other animals. However, not all viruses are pathogenic in humans and can provide useful services to science.

Most of the viruses identified in by Hartmann and her team are known as bacteriophages. Rather than being a hazard to humans, these phages infect bacteria.

In the newly published study in the journal Frontiers in Microbiomes, Hartmann's research group observed that most Americans spend two-thirds of their lives in their homes, and so learning about the organisms that occupy this shared space is valuable to understanding the quality of living spaces.

What's living on your toothbrush?

To understand the makeup of viral communities, the researchers used previous data obtained by citizen science projects that swabbed showerheads and toothbrushes in US homes. They then assessed the makeup of these environments, finding very different microbial communities in each location.

While viruses are usually considered to exist in a kind of living-dead nether zone, where they require a living host to reproduce and, occasionally, cause harm, they nevertheless inhabit many different environments in complex communities.

Inside American bathrooms, Hartmann's team found more than 600 unique viral species living on showerheads and toothbrush bristles.

Their diversity was such that no one showerhead community matched any other. The same went for comparisons between the toothbrushes.

It's hoped that the bacteriophage viruses identified by her research group could open new avenues for bacterial infection treatments and serve as a more appropriate way to cleanse environments without antimicrobial products.

"The more you attack them with disinfectants, the more they are likely to develop resistance or become more difficult to treat," said Hartmann.

"We should all just embrace them. Microbes are everywhere, and the vast majority of them will not make us sick."

Showerhead bacterial communities are a different story

It should come as little surprise that watery environments are brimming with life. After all, water is top of the search list for scientists looking for life on other planets.

As well as viruses and bacteriophages, these bathroom surfaces can also harbor bacteria and fungi, as discovered by other research efforts.

Three years ago, Hartmann's group started its research into the topic, dubbing it "Operation Pottymouth" as it tried to investigate the long-held claim that flushing a bathroom toilet sends a haze of fecal aerosols onto your toothbrush.

That claim, they argued, probably wasn't true. Instead, most toothbrush bacteria appeared to come from its user's mouth.

In 2018, results from the Showerhead Microbiome Project found associations between mycobacterium-infected showerheads in American and European bathrooms and prevalence of lung infections.

Fortunate, then, that Hartmann's latest research found the bacteriophages most commonly found in these environments tend to target harmful mycobacteria.

"We could envision taking these mycobacteriophage and using them as a way to clean pathogens out of your plumbing system," Hartmann said.

"We want to look at all the functions these viruses might have and figure out how we can use them."

Edited by: Rob Mudge

Primary source:

Stefanie Huttelmair, Weitao Shuai, Jack T. Sumner, Erica M. Hartmann (2024). Phage communities in household-related biofilms correlate with bacterial hosts. Frontiers in Microbiomes. https://doi.org/10.3389/frmbi.2024.1396560

Additional sources:

Matthew J. Gebert et al (2018). Ecological Analyses of Mycobacteria in Showerhead Biofilms and Their Relevance to Human Health. mBio. https://doi.org/10.1128/mbio.01614-18

Ryan A. Blaustein et al (2021). Toothbrush microbiomes feature a meeting ground for human oral and environmental microbiota. Microbiome. http://dx.doi.org/10.1186/s40168-020-00983-x