Which bacteria hang out in belly buttons? Here’s a who’s who | Science News for Students

Which bacteria hang out in belly buttons? Here’s a who’s who

As people age, they have more types — but fewer bugs overall
May 15, 2018 — 5:09 pm EST
belly button

What’s in your belly button? Not just lint. A teen did some science to find out what microbes were living in people’s navels.


PITTSBURGH, Pa. — For Kathleen Schmidt, 18, the biggest challenge in her research was finding people willing to swab their belly buttons. Her tiny town of Ashley, N.D., has only 600 residents — and most weren’t too willing to bare their bellies for science. “I got a lot of no’s,” the teen recalls. “Even my sister wouldn’t let me swab hers.” But with a lot of begging, the senior at Ashley Public School got her volunteers. She used swabs of their belly buttons to create a who’s who of the microbes living on — and in — our navels.

Belly buttons — or navels — are leftovers. They mark the spot where the umbilical cord once linked mother and child. As the baby was developing in the womb, the umbilical cord served as the pipeline delivering food and oxygen. It also carried away wastes.

After birth, the umbilical cord gets cut, leaving behind a scar affectionately known as the belly button. Some people have navels that are little hollows, sometimes called “innies.” Others have belly buttons that stick out, called “outies.” All are good spots for bacteria to hang out. “Because it’s warm and moist,” Kathleen notes, “a belly button is the perfect place for bacteria to grow, especially innies.”

The microbes living in navels are part of their hosts’ microbiome — the community of microscopic organisms such as bacteria, viruses and fungi that live on and in all animals and plants. Some types of microbes can cause illness. Many can help protect the body from other, nasty bacteria. 

“I love people and I also love bacteria a lot,” Kathleen says, and “I wanted to do a project where I could combine them both.” While she was reading scientific papers, she came across a study by Robert Dunn. He’s an ecologist at North Carolina State University in Raleigh. And in 2012, his team published a paper in the journal PLOS ONE. They, too, had been studying the microbes that lived in belly buttons. “It inspired me, the stuff he found,” Kathleen explains. “I wanted to find some of this stuff!”

belly button bacteria
One navel produced this rich and colorful bacterial growth.
K. Schmidt

After asking around her town for three weeks, the teen came up with 40 volunteers. There was an even mix of males and females. Kathleen also selected her navels carefully, dividing them into four age groups, with 10 people in each. The recruits swabbed their belly buttons. Kathleen then rubbed the swabs on agar plates — plastic disks filled with a gel that bacteria like to eat.

The teen kept her plates in an incubator for three days at roughly body temperature: 37.5° Celsius (or 99.5° Fahrenheit). Then she drove her plates several hours to the University of Mary in Bismarck, N.D. There, with the help of biologist Christine Fleischacker, Kathleen used a microscope to identify and count the microbes growing on her plates.

“I found a lot of bacteria,” she says. “Most of it was Bacillus [a genus of bacteria] which is very good. If you want a bacterium in your bellybutton — and you do — it’s Bacillus. It…fights off bad bacteria.” Kathleen also found bacterial from other genuses, which are groups of closely related species. These included Staphylococcus (or staph). This germ can cause disease if it gets into the wrong places. Many of the bacteria she found in her navel samples were similar to bacteria that Dunn and his group had reported before.

Who has which belly button bugs?

Most of the time, there was no difference between males and females, the teen found. The exception? Women ages 14 to 29 harbored fewer bacteria than did men in their age group. And for good reason. “When I asked how many of [the volunteers] cleaned their bellybuttons, all 5 females said they did,” Kathleen recalls. “Only two of the males said they cleaned on the daily.”

The biggest differences were not a matter of whether the hosts were clean or dirty, but instead their age. Adult volunteers had many more types of bacteria in their navels. But while the communities inhabiting adult navels were more diverse, children had belly buttons with many more individual bacteria.

Kathleen Schmidt with mentor
Kathleen (left) goes over her results with her mentor Christine Fleischacker.
K. Schmidt

And what about the outies and innies? “Outies primarily only have Bacillus and staph,” she says. Innies tended to have more diverse mixes of bacteria. One even harbored a fungus.

Kathleen shared her navel results here, this week, at the Intel International Science and Engineering Fair (ISEF). Created by Society for Science & the Public, or SSP, and sponsored by Intel, the competition this year brought together students from 81 countries. The nearly 1,800 competitors showed off the science-fair projects that won them a spot as a finalist at this year’s event. (SSP also publishes Science News for Students and this blog).

It may seem like silly science, but in fact it’s important to figure out which bacteria live on our skin. “People should be aware of what’s on their body, how it affects them and the world,” Kathleen says.

“This is amazing,” Dunn says, after learning of the work he inspired in Kathleen. “I love that she thought to focus in on things we missed.”

The teen’s project has only made her love of microbes stronger. “This is what I’m going to do for the rest of my life,” she says. “I love it so much.” She’s already gotten a job for the fall, when she starts college at North Dakota State University in Fargo. She’ll be working in a microbiology lab, of course.

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Power Words

(for more about Power Words, click here)

agar     A gelatinous material made from certain marine algae used as a material (and food source) in which to grow bacteria.

bacteria     (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).

bacterial     Having to do with bacteria, single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.

biology     The study of living things. The scientists who study them are known as biologists.

blog     Short for web log, these internet posts can take the form of news reports, topical

colleague     Someone who works with another; a co-worker or team member.

ecology     A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

engineering     The field of research that uses math and science to solve practical problems.

fungus     (plural: fungi) One of a group of single- or multiple-celled organisms that reproduce via spores and feed on living or decaying organic matter. Examples include mold, yeasts and mushrooms.

gel     A gooey or viscous material that can flow like a thick liquid.

genus     (plural: genera) A group of closely related species. For example, the genus Canis — which is Latin for “dog” — includes all domestic breeds of dog and their closest wild relatives, including wolves, coyotes, jackals and dingoes.

Intel International Science and Engineering Fair     (Intel ISEF) Initially launched in 1950, this competition is one of three created (and still run) by the Society for Science & the Public. Each year now, approximately 1,800 high school students from more than 75 countries, regions, and territories are awarded the opportunity to showcase their independent research at Intel ISEF and compete for an average of $4 million in prizes. 

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microbiology     The study of microorganisms, principally bacteria, fungi and viruses. Scientists who study microbes and the infections they can cause or ways that they can interact with their environment are known as microbiologists.

microbiome     The scientific term for the entirety of the microorganisms — bacteria, viruses, fungi and more — that take up permanent residence within the body of a human or other animal.

microscope     An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

microscopic     An adjective for things too small to be seen by the unaided eye. It takes a microscope to view objects this small, such as bacteria or other one-celled organisms.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

Society for Science & the Public   A nonprofit organization created in 1921 and based in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: the Regeneron Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

staph     Short for Staphylococcus aureus. It's a species of bacteria that is responsible for a number of serious human infections. It can cause surface abscesses, or boils. If it gets into the bloodstream, where it can be carried throughout the body, it may also cause pneumonia and infections of the joints or bones.

waste     Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.

womb     Another name for the uterus, the organ in mammals in which a fetus grows and matures in preparation for birth.


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