Your Toothbrush and Showerhead Are Covered in Viruses

Researchers from Northwestern University have uncovered a hidden world of "untapped biodiversity" in our homes, identifying over 600 distinct viruses from toothbrushes and showerheads. The study, published in Frontiers in Microbiology, highlights the unique and diverse viral communities in our built environments and their potential implications for human health.

A hidden trove of microorganisms

Microbes inhabit every corner of our environment, often going unnoticed. From the soil beneath our feet to the air we breathe, billions of microorganisms play a role in the ecosystems around us. Although many microbial niches are well-documented, we tend to forget the communities that reside in our built environments. The average American spends 93% of their time in indoor environments, with nearly 70% of that time spent at home. These niches may be serving as a source of microbial exposure to humans, including the transmission of potential pathogens.

Dr. Erica M. Hartmann, associate professor of civil and environmental engineering and medicine at Northwestern University, and colleagues previously characterized bacteria found living on used toothbrushes and samples collected from showerheads. The new study, which Hartmann co-authored, utilized the same samples to identify and characterize viruses.

“This project started as a curiosity. We wanted to know what microbes are living in our homes. If you think about indoor environments, surfaces like tables and walls are really difficult for microbes to live on. Microbes prefer environments with water. And where is there water? Inside our showerheads and on our toothbrushes,” said Hartmann.

Despite their prevalence, research into the viral populations in everyday settings has been limited, particularly studies on bacteriophages – viruses that specifically target bacteria. These microbes have recently entered the spotlight due to their potential use in treating antibiotic-resistant bacterial infections.

Hartmann and colleagues selected 92 showerheads and 34 toothbrush samples from their previous study for further metagenomic sequencing. After characterizing the bacteria, the team used DNA sequencing to examine the viral population in the samples.

No two samples were alike

Over 600 viruses across the 126 samples, many of which were novel and uncharacterized, were identified.

“The number of viruses that we found is absolutely wild. We found many 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,” said Hartmann.

Surprisingly, the team found that no two samples were alike.

“We saw basically no overlap in virus types between showerheads and toothbrushes. We also saw very little overlap between any two samples at all. Each showerhead and each toothbrush is like its own little island. It just underscores the incredible diversity of viruses out there,” said Hartmann.

Mycobacteriophages – the pathogen fighters we didn’t know we needed

Hartmann and team observed a higher number of mycobacteriophages, which infect mycobacteria, compared to any other phage type in the samples. This pathogenic bacteria species is linked with leprosy, tuberculosis and chronic lung infections.

“We could envision taking these mycobacteriophage and using them as a way to clean pathogens out of your plumbing system. We want to look at all the functions these viruses might have and figure out how we can use them,” said Hartmann.

Most microbes are safe

Although the team found a large number of novel microbes, they did not find any evidence these viruses carried antibiotic-resistance genes or harmful virulence factors.

“Microbes are everywhere, and the vast majority of them will not make us sick. The more you attack them with disinfectants, the more they are likely to develop resistance or become more difficult to treat. We should all just embrace them,” said Hartmann.

The diverse range of phages and their genetic functions warrant further investigation to understand their potential impact on human health and their possible applications in biotechnology or medical treatments.

Given the limited data available from built environments, Hartmann noted that future research could look to compare these viral communities to those found in natural or engineered settings, like wastewater systems, which have been more extensively studied.

Reference: Huttelmaier S, Shuai W, Sumner J, Gebert M, Fierer N, Hartmann EM. Phage communities in household-related biofilms correlate with bacterial hosts. Front Microbio. 2024;3. doi : 10.3389/frmbi.2024.1396560

This article is a rework of a press release issued by Northwestern University. Material has been edited for length and content.