Your toothbrush is teeming with hundreds of types of viruses

Hundreds of viruses that infect bacteria have been found on toothbrushes and showerheads. This isn’t something to be worried about, though, because the viruses aren’t harmful to humans and studying how they work could reveal new ways to kill drug-resistant bacteria.

It is already known that our toothbrushes and showerheads are full of bacteria from our mouths and from water supplies. But we know little about the viruses that also dwell on these surfaces.

To gain a better picture, Erica Hartmann at Northwestern University in Illinois and her colleagues swabbed 92 showerheads and 36 toothbrushes from the bathrooms of people living in the US.

By sequencing the DNA from the swabbed samples, the researchers discovered more than 600 viruses known to infect bacteria, called bacteriophages. Most of the viruses, which aren’t harmful to humans, came from the toothbrushes, and many hadn’t been described before. “That’s wild, it just underscores how much novel stuff is out there,” says Hartmann.

The researchers didn’t test whether the viruses are affecting the thousands of bacteria that they also found, but a bacteriophage tends to do one of two things, says Hartmann. It might hijack the molecular machinery of a bacterium to make copies of itself, and then kill the bacterium as it exits. Or it can integrate into the bacterial genome and change how bacteria behave.

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The bacteriophages that Hartmann and her colleagues identified are probably present on any moist surface around the home, such as sinks and inside fridges. “We would absolutely expect them anywhere,” she says.

“It’s a fascinating resource that allows us to better understand the breadth and the details of phage activity inside a home,” says Jack Gilbert at the University of California, San Diego.

Because engineered bacteriophages can be used to kill drug-resistant bacteria when antibiotics fail, the discovery of so many new ones could point the way to more treatments, says Dirk Bockmühl at the Rhine-Waal University of Applied Sciences in Germany.